I have faced a version of this decision myself. There is some extra money available, unused TFSA room waiting to be filled, and a mortgage balance that could be knocked down. The money has to go somewhere. Do I put another $25,000 into investments, or send it against the house?

At first, this looks like one of the simpler decisions in personal finance. Compare the mortgage rate to the expected investment return. If the investments should earn more, invest. If the mortgage costs more, pay it down. It is an attractive rule because it fits in one sentence, but the more I thought about the decision, the less useful that sentence became.

A Canadian homeowner with a 5% mortgage is not really choosing between a guaranteed 5% investment and an investment expected to earn 8%. Paying down a mortgage is not literally an investment, equities do not produce their expected return on schedule, and the mortgage rate itself will eventually renew. There are balance-sheet differences as well. TFSA money remains a financial asset that can be sold and accessed, while money sent against the mortgage becomes home equity. A household may already have most of its net worth tied up in its house, or it may have a large investment portfolio and relatively little reason to add another $25,000 to it. The same decision can look completely different depending on what surrounds it.

There is, however, a very useful financial comparison underneath all of this. In Canada, interest on an ordinary principal-residence mortgage is generally paid with after-tax dollars and is not deductible. The CRA’s rules on interest deductibilitygenerally require borrowed money to be used for an income-earning purpose before the interest becomes deductible. Investment income and growth inside a TFSA, meanwhile, are generally tax-free. That gives us something unusually close to an apples-to-apples comparison: if I pay down a 5% mortgage, I avoid roughly a 5% after-tax borrowing cost; if I invest inside a TFSA and earn 8%, I keep roughly the full 8%.

The interesting question is therefore not which number is bigger. It is how much more return I should demand before voluntarily accepting market risk instead of taking the certainty of reducing the mortgage. That is where this becomes a much more interesting capital-allocation problem.

A TFSA Is an Account, Not an Investment

Before comparing a mortgage to a TFSA, there is an important distinction to make. A TFSA is not an investment. It is an account that can hold many different investments, and those investments produce radically different comparisons with a mortgage.

In 2026, the annual TFSA contribution limit is $7,000, while unused contribution room carries forward. Someone who has accumulated room from previous years may therefore be able to contribute $25,000, $50,000 or considerably more at once. Inside the account, that money could sit in cash, a high-interest savings account or GICs. It could also be invested in bonds, a balanced portfolio or a globally diversified equity portfolio.

Consider someone with a 5.5% mortgage who says they are debating whether to put $25,000 into their TFSA. If that TFSA is going to earn 3.5% in cash, the financial comparison is not especially difficult. They are deliberately carrying debt at 5.5% so they can own an asset yielding 3.5%. There may still be a reason to do that because liquidity has value, but there is no investment-return argument for it.

Change the TFSA asset to a globally diversified equity portfolio that will be held for 25 years and the decision changes completely. The expected return may be materially higher than the mortgage rate. The homeowner has accepted volatility and uncertainty in exchange for the possibility of much greater long-term compounding. It is the same TFSA, but an entirely different alternative to mortgage prepayment. Any rule that says “TFSA beats mortgage” without asking what is actually inside the TFSA misses the most basic part of the question.

The Mortgage Has an After-Tax Hurdle Rate

For an ordinary Canadian principal residence, mortgage interest is generally not tax deductible. You earn income, pay tax on it, and use what remains to service the mortgage. That makes eliminating mortgage interest unusually valuable.

Suppose the mortgage costs approximately 5%. If I put $25,000 against the principal, I no longer pay interest on that $25,000. Economically, that behaves a lot like receiving a guaranteed after-tax return equal to the borrowing cost I avoided. The word like matters because a mortgage prepayment is not literally an investment earning 5%. There is no account producing a return; I have reduced a liability. The benefit appears as interest I never have to pay and greater equity in the house.

From the perspective of household net worth, though, the analogy is useful. If I can either earn 4% tax-free somewhere or avoid a 5% non-deductible borrowing cost, avoiding the 5% cost puts me ahead. Because both sides of the TFSA-versus-principal-residence-mortgage comparison are effectively after-tax, there is also less tax noise than there would be if I were comparing the mortgage with a taxable investment account.

There is a small Canadian wrinkle here. Fixed mortgage rates are commonly quoted using semi-annual compounding, so a quoted 5% mortgage has an effective annual cost slightly above 5%, at roughly 5.06%. That difference is not going to change anyone’s life, and I would still describe it conversationally as a 5% mortgage. But if we are going to model the decision, we might as well model it properly.

What the $25,000 Math Actually Says

Take a $25,000 lump sum and compare the future economic value of using it to reduce the mortgage with investing it inside a TFSA. On the mortgage side, I am treating the avoided borrowing cost as the economic return. On the TFSA side, I am assuming the stated investment return actually compounds at that rate. That second assumption is obviously much less certain when we are talking about equities, which is exactly why the mathematical winner is not necessarily the practical winner.

Rate or return	5 years	10 years	20 years
3% mortgage prepayment	$29,013	$33,671	$45,350
4% mortgage prepayment	$30,475	$37,149	$55,201
5% mortgage prepayment	$32,002	$40,965	$67,127
6% mortgage prepayment	$33,598	$45,153	$81,551
7% mortgage prepayment	$35,265	$49,745	$98,982
TFSA earning 4%	$30,416	$37,006	$54,778
TFSA earning 6%	$33,456	$44,771	$80,178
TFSA earning 8%	$36,733	$53,973	$116,524
TFSA earning 10%	$40,263	$64,844	$168,187

The obvious lesson is what compounding does to relatively small differences in return. At 3%, the future economic value of that $25,000 is about $45,000 after twenty years. At 8%, the TFSA reaches more than $116,000. That is why very cheap debt combined with long-term equity investing can be such a powerful strategy.

The less obvious lesson is how quickly that advantage narrows as the mortgage rate rises. At a 7% mortgage rate, the same $25,000 represents almost $99,000 of avoided future borrowing cost after twenty years under this simplified model. An 8% TFSA return gets to about $116,500. Equities still win on expected terminal value, but the expected advantage is nowhere near as overwhelming as it was against a 3% mortgage.

The mathematical break-even is easy to calculate. If the mortgage effectively costs 5.06% and the TFSA compounds at exactly 5.06%, the simplified result is essentially a tie. I don’t think that is a particularly useful decision rule, though, because expected return and guaranteed cost avoidance are not interchangeable just because both can be expressed as percentages.

Suppose I expect an equity portfolio to return 5.5% while my mortgage costs 5%. Do I really want to accept the possibility of a major market decline, years of disappointing returns and an uncertain terminal value in exchange for an expected return only slightly higher than the borrowing cost I can eliminate with certainty? I would not.

The numbers illustrate how small that advantage really is. On a $25,000 lump sum, a TFSA earning 5.5% has an expected advantage over a 5% mortgage of only about $1,700 after ten years and $5,800 after twenty. At 6%, the advantage grows to around $3,800 after ten years and $13,000 after twenty. At 7% and 8%, the differences finally start becoming substantial.

Expected TFSA return	Approx. advantage over 5% mortgage after 10 years	Approx. advantage after 20 years
5.5%	$1,700	$5,800
6%	$3,800	$13,100
7%	$8,200	$29,600
8%	$13,000	$49,400

This is where I think the usual “invest if your expected return is higher than your mortgage” advice falls apart. A 5.5% expected return technically beats a 5% mortgage, but the investment needs to do more than win in a spreadsheet. It needs to compensate me for uncertainty.

How Much Extra Return Is Enough?

There cannot be one universal risk premium because a 30-year-old investing for retirement is not taking the same economic risk as a 64-year-old who expects to start drawing the money next year. Still, I think a practical framework is possible.

I would start by treating the mortgage rate as the hurdle. If the mortgage effectively costs 5% and the investment is expected to return 6%, I have roughly a one-percentage-point expected advantage. That is not very exciting. At 7%, the expected spread is around two points and the decision becomes more interesting. At 8%, there are roughly three points of expected return to compensate for accepting volatility, which starts to feel like a meaningful investment proposition rather than an attempt to squeeze an extra fraction of a percentage point from the balance sheet.

Expected investment return above mortgage cost	How I would view it
Less than 1 percentage point	Mortgage is extremely competitive
1–2 points	Genuine grey zone
2–3 points	TFSA equities become increasingly attractive over a long horizon
3–4 points	Stronger long-term investment case
4+ points	Compelling expected-return advantage if the investor can tolerate the risk

This is not a financial law, and I would not want it repeated as one. It is simply a way to stop pretending that 6% and 5% are meaningfully different because one number happens to be larger. The horizon matters just as much as the spread. Over five years, I would be uncomfortable building a financial plan around an assumed 8% equity return because five-year periods can produce miserable market results. Over twenty or thirty years, I am much more willing to accept volatility in exchange for a meaningful expected return premium.

Mortgage rate is therefore one of the most powerful variables in the entire decision. Against an assumed 8% TFSA return over twenty years, a 3% mortgage leaves the TFSA with an expected advantage of roughly $71,000 on our $25,000 starting amount. At a 5% mortgage, that falls to about $49,000. At 7%, the expected advantage is only around $17,500. That is still real money, but now I am accepting two decades of equity-market uncertainty to beat something economically very close to a guaranteed 7% after-tax return.

This is why investment advice that made perfect sense when homeowners were carrying mortgages in the 2% range becomes much less compelling when borrowing costs move higher. For me, roughly 4% to 5% is where the decision becomes genuinely interesting. At 2% to 3%, I would need a fairly good reason not to favour long-term diversified investing if the household is liquid and the money really is long term. At 6% to 7%, I would need a fairly good reason to pass on mortgage reduction. That reason may exist, but the mortgage is no longer a trivial opponent.

Your Mortgage Rate Has an Expiry Date

There is another distinctly Canadian problem with comparing today’s mortgage rate against a twenty-year expected investment return: the mortgage probably does not have today’s rate for twenty years. The amortization may be twenty or twenty-five years, but the mortgage term is normally much shorter.

Suppose I have a 3% mortgage that renews in twelve months. It would be misleading to compare an 8% equity return over twenty years against a 3% mortgage cost over the same twenty years because I do not own twenty years of 3% financing. I own one more year. After that, the debt will be repriced, and if the next mortgage costs 5%, 5.5% or 6%, paying down principal today saves interest at that future rate as well.

A homeowner locked into 3% for another four years is therefore in a very different position from someone at 3% who renews next spring. Both can truthfully say, “My mortgage rate is 3%,” but economically they do not own the same liability. This does not mean we need to predict future mortgage rates. It simply means today’s rate should not automatically be extrapolated across a long-term investment horizon.

Six Versions of the Same $25,000 Decision

The easiest way to see how much the answer can move is to keep the $25,000 constant and change the circumstances around it.

A 3% Mortgage and a Twenty-Year Equity Horizon

Start with a 3% mortgage and a diversified equity portfolio inside the TFSA that will be held for twenty years. At an assumed 8% compound return, the TFSA reaches roughly $116,500, while the economic value of avoiding the 3% mortgage cost is around $45,000. That is an enormous expected gap, with a substantial cushion even if future equity returns disappoint relative to the 8% assumption.

For a disciplined long-horizon investor who already has adequate emergency reserves, this is a strong TFSA case. I would still look at mortgage renewal timing and overall debt load, but I would be reluctant to sacrifice decades of tax-free equity compounding simply to eliminate very cheap debt. The same long-duration compounding logic sits behind ideas such as Coast FIRE for Canadians: capital invested early has a very long runway to do the heavy lifting.

A 5% Mortgage and Ten to Twenty Years

Move the mortgage to 5%. At an assumed 8% return, the TFSA reaches roughly $54,000 after ten years compared with an economic mortgage-prepayment value of about $41,000, giving the TFSA an expected advantage of approximately $13,000. After twenty years, that expected advantage approaches $49,000.

At ten years, I consider this genuinely debatable. At twenty years, I would lean more toward TFSA equities for a household with strong liquidity, a long horizon and the temperament to leave the money alone. But I would not describe paying down the mortgage as financially unsophisticated. A guaranteed reduction in a roughly 5% after-tax borrowing cost is a respectable use of capital. The equity investor is accepting risk in pursuit of a higher return; the mortgage payer is accepting a lower expected terminal value in exchange for certainty. Both can be rational.

A 6.5% Mortgage and a Conservative TFSA

Now assume the mortgage is 6.5% and the TFSA money would go into a 4% GIC or similarly conservative investment. After ten years, the mortgage-prepayment equivalent is roughly $47,000 while the 4% TFSA reaches about $37,000. After twenty years, the gap becomes enormous.

Unless there is a strong liquidity reason to keep the capital accessible, deliberately earning 4% while carrying a non-deductible liability costing more than 6.5% is difficult to defend. The mortgage wins. This is why “I always max the TFSA first” can become just as dogmatic as “all debt is bad.” Maxing an account is not the objective; improving the balance sheet is.

A 6.5% Mortgage and a Twenty-Five-Year Equity Portfolio

Change only the TFSA investment and the conclusion becomes less obvious. If the $25,000 goes into diversified equities with an assumed 8% return, the TFSA still beats the 6.5% mortgage in expected terminal wealth. After twenty years, the expected advantage is roughly $27,000; after twenty-five years, it approaches $47,000.

The important number, though, is the spread. An 8% expected equity return is only about 1.4 percentage points above the effective cost of a 6.5% mortgage. That is not a wide risk premium. I can defend choosing equities for a young investor with excellent liquidity, a high tolerance for volatility and decades to invest. I can just as easily defend taking the mortgage reduction. At this borrowing cost, certainty becomes extremely valuable, and this may be the clearest example of why “stocks should return more” is not enough.

When the $25,000 Is Almost All the Cash You Have

This scenario can override almost everything the spreadsheet says. Suppose I have $25,000 available, almost no other liquid savings and a 6% mortgage. The mathematical comparison favours the mortgage, but I would be very reluctant to send the entire $25,000 into the house.

That money may need to cover a job loss, a furnace, a vehicle, a roof, a family emergency or simply the ordinary unpredictability of life. Home equity is wealth, but it is not cash. Once the money goes against the mortgage, accessing it again may require a refinance, a HELOC, lender approval or borrowing at whatever interest rate exists at the time. A HELOC certainly improves optionality, but it is not identical to holding liquid assets. Credit can be repriced, limits can change and qualification matters.

This is where the broader idea of financial sovereignty enters the decision for me. I do not define financial strength only as having the highest possible net worth. It also means having room to manoeuvre. A household that owns an expensive house, has aggressively paid down its mortgage and has almost no liquid capital can look extremely safe on paper while being surprisingly fragile in practice. I wrote about this more broadly in House Rich in Canada: The Hidden Risks of Concentration.

When the Investment Portfolio Is Already Large

Now reverse the situation. Suppose the household already has substantial TFSA, RRSP and non-registered assets, plus a healthy emergency reserve, but still carries a large mortgage. Another $25,000 in the portfolio may barely change the diversification of the household, while a $25,000 mortgage prepayment reduces leverage and future fixed expenses.

This household may rationally prefer debt reduction even if equities still have a somewhat higher expected return. The objective is no longer simply to maximize the terminal value of the next $25,000; it is to improve the resilience of the entire balance sheet. For anyone who expects to refinance, move or borrow again, reducing mortgage debt may also improve the lending side of that balance sheet. I have covered the mechanics of Canadian GDS and TDS debt ratiosseparately.

The House-Rich Problem and the Value of Liquidity

Canadian households are particularly prone to concentrating wealth in their principal residence. It is easy to understand why. Housing has historically been culturally reinforced as both consumption and investment, mortgage payments happen automatically, and home equity builds quietly. Financial investing, meanwhile, often feels discretionary. A homeowner can therefore reach midlife with several hundred thousand dollars of equity and surprisingly little outside the house.

Imagine someone who owns a $1 million house with a $500,000 mortgage and has only $50,000 invested. Their net home equity is already $500,000. If another $50,000 goes against the mortgage, home equity rises to $550,000 while financial assets remain at $50,000. If the same money goes into a diversified TFSA, home equity remains $500,000 and financial assets rise to $100,000. The household has roughly the same starting net worth either way, but it does not have the same balance sheet. The second version has more liquidity, more diversification and less dependence on the value and accessibility of one piece of Canadian real estate.

Now give the same homeowner a $1.5 million investment portfolio and the argument changes again. Another $50,000 in equities barely affects diversification, while reducing the mortgage may materially improve the household’s debt position. This is why I don’t think mortgage versus TFSA can be answered sensibly by looking at the $25,000 in isolation. What matters is what that dollar does to the entire household balance sheet.

Liquidity deserves particular attention because traditional return comparisons handle it poorly. If I invest $25,000 inside a TFSA, I can generally sell the investment and withdraw the money when I need it. If I pay down the mortgage, I may improve net worth by the same starting amount, but the capital is embedded in the house. There is no clean percentage return I can assign to having $25,000 accessible during a job loss, but that does not make the optionality worthless.

Businesses understand this instinctively. They often hold cash while simultaneously carrying debt because pure return maximization is not the only objective; survival and flexibility matter too. A household should think the same way. I would separate the decision into two questions: how much liquidity does the household reasonably need, and what should happen to the capital above that level? The first $25,000 of savings may belong somewhere completely different from the next $25,000.

You Don’t Lose Unused TFSA Room, But You Do Lose Time

Another common argument is that the TFSA should always come first because unused room will otherwise be lost. That is not how TFSA contribution room works. Unused room carries forward, so if I have $25,000 of available room and send $25,000 against the mortgage this year, I still have that TFSA room later.

What I have lost is time. If the $25,000 could have compounded tax-free for ten years before I eventually filled the room, that tax-free compounding opportunity is gone. The distinction matters because the economic cost depends heavily on whether I am realistically going to fill the room later. Someone generating substantial annual savings may catch up on unused TFSA room quickly. Someone who struggles to produce $5,000 of surplus cash each year could leave the room unused for another decade. The legal contribution room survives in both cases, but the economic result is very different.

TFSA withdrawals add another layer of flexibility. Under the CRA’s TFSA withdrawal rules, amounts withdrawn are generally added back to contribution room at the beginning of the following calendar year. That makes the TFSA unusually useful as a pool of long-term capital, although it also creates a behavioural temptation that home equity does not have to the same degree.

Behaviour Can Overrule the Spreadsheet

Suppose two people each put $25,000 into a TFSA equity portfolio. The first leaves it invested for twenty years. The second withdraws $8,000 for a vehicle, another $4,000 for a vacation, sells part of the portfolio during a bear market and gradually spends the rest. The mathematical model says both chose the TFSA strategy. In practice, only one of them actually executed it.

Mortgage prepayment has an underrated behavioural advantage because it creates friction. Once the money is in the house, getting it back normally requires a deliberate borrowing decision. Anyone with a HELOC knows that does not make home equity impossible to spend, but there is still an additional step. For some people, that friction is extremely valuable. For a disciplined investor, on the other hand, TFSA assets can remain untouched for decades while still providing useful liquidity if something genuinely important happens.

The behavioural question is therefore not whether debt reduction is morally superior to investing. It is which form of capital you are actually more likely to leave alone. There is a behavioural trap on the mortgage side too: someone makes a $25,000 prepayment, feels financially virtuous and then gradually expands lifestyle spending because the balance sheet feels safer. If debt reduction simply creates permission to consume more elsewhere, the long-term result may look very different from the model. Strategies only work if we actually execute the behaviour they assume.

The Answer Changes as You Get Older

A young household has one enormous advantage in this comparison: time. Thirty years of tax-free equity compounding can overwhelm relatively cheap mortgage interest. Young households, however, also often have the weakest liquidity. They may have young children, large mortgages, uncertain career paths and major future expenses. That makes aggressive mortgage prepayment less obviously safe than it first appears. Building liquid financial assets may be more valuable than trying to eliminate every dollar of mortgage debt as quickly as possible.

Mid-career is where I think the decision becomes most interesting. Income is usually higher, the investment portfolio has had time to grow, the mortgage may still be substantial, children and education costs compete for savings, and retirement is no longer an abstraction. At this point, I would start thinking about the next $25,000 as part of a genuine allocation problem. How much home equity do I already have? How much financial capital? How exposed am I to the next mortgage renewal? How much fixed monthly expense do I want ten years from now? The correct answer can quite reasonably change from year to year.

Approaching retirement, the case for debt reduction becomes stronger even if the spreadsheet still gives equities a higher expected terminal value. A household without a mortgage requires less cash flow. That reduces the amount that must be withdrawn from investments, reduces pressure to sell assets during a bad market and lowers the income target required to fund retirement. This matters whether the objective is conventional retirement or some version of financial independence in Canada, because lowering permanent spending also lowers the amount the investment portfolio ultimately has to support.

This is where the preference for entering retirement mortgage-free can have a perfectly rational financial foundation rather than being merely psychological. At the same time, I would not turn “mortgage-free before retirement” into another absolute rule. A retired household with a 2% mortgage, several million dollars invested and abundant cash may gain very little by liquidating assets simply to satisfy an ideological preference for zero debt. The balance sheet still matters more than the slogan.

Sequence-of-returns risk also becomes more relevant at this stage. If I am 35, put $25,000 into a TFSA and do not touch it for thirty years, the order of annual market returns matters much less than it does for someone actively withdrawing from a portfolio. For someone approaching retirement, carrying a mortgage increases the cash flow the portfolio must produce during those early years. Reducing that fixed expense can therefore reduce the need to sell investments during a bad market even when long-run expected equity returns remain higher.

What Changes Once the TFSA Is Full?

The comparison becomes less favourable to investing once the alternative moves from a TFSA to a non-registered account. Inside the TFSA, investment growth is generally tax-free. Outside it, the form of return matters. Interest income is taxed, foreign income can create tax drag, Canadian dividends receive their own tax treatment, and realized capital gains are taxed according to the rules in force when they occur.

That means a 6% nominal return in a taxable account is not necessarily a 6% return to the household. Meanwhile, avoiding a 5% principal-residence mortgage cost still saves roughly 5% in after-tax dollars. The mortgage hurdle has not changed, but the competing investment’s after-tax return has fallen. This is one reason TFSA versus mortgage is the cleanest version of the debate.

Once the TFSA and other appropriate registered options are full, I become more demanding about the expected return required from taxable investing before voluntarily carrying expensive non-deductible mortgage debt. The exact calculation depends on the investment and the household’s tax situation, but the underlying principle is straightforward: tax drag raises the investment hurdle.

This Is Not the Smith Manoeuvre

There is a related strategy that sometimes gets dragged into this discussion: the Smith Manoeuvre. It is not the same decision. The Smith Manoeuvre attempts to convert non-deductible mortgage debt into potentially deductible investment debt by borrowing for the purpose of investing in income-producing assets. I covered that separately in The Smith Maneuver: A Deep Dive for Canadians Who’ve Already Read the Hype.

Here, I am assuming the $25,000 already exists. The choice is simply whether to use existing cash to reduce non-deductible debt or invest unleveraged inside a TFSA. That is a much cleaner capital-allocation problem.

So Where Would I Put the Next $25,000?

After running the numbers, I think there is a useful way to frame the decision without pretending there is one universal answer.

At a mortgage rate around 2% to 3%, I would generally favour long-term TFSA equity investing if I had adequate liquidity, unused TFSA room and at least fifteen to twenty years before needing the money. The expected return spread is simply too attractive to ignore. I would still prepay the mortgage if the household was overleveraged, approaching retirement or psychologically incapable of leaving the investment alone, but cheap mortgage debt does not bother me much when the alternative is decades of tax-free diversified investing.

At roughly 4% to 5%, I start paying much closer attention. This is the real decision zone. If my mortgage costs 5% and my realistic investment expectation is only 6%, I would lean toward the mortgage because I am not interested in taking meaningful market risk for a one-point expected spread. With a twenty-plus-year horizon and a reasonable expectation of something closer to 7% or 8% from a diversified equity portfolio, the TFSA becomes much more compelling. Even there, liquidity and household concentration can legitimately change the answer.

At 6% to 7%, the mortgage becomes a formidable competitor. A guaranteed reduction in a non-deductible borrowing cost at those rates is an exceptionally strong low-risk use of capital. If the TFSA alternative is cash, GICs or conservative fixed income, I would generally pay down the mortgage once appropriate liquidity was preserved. If the alternative is diversified equities and I have twenty-five years to invest, there is still a legitimate TFSA case, but I would want a meaningful expected risk premium. An 8% expected return against a 6.5% mortgage is not the slam dunk some investing discussions make it sound like; it is a relatively narrow expected spread between an uncertain asset and a very expensive guaranteed liability.

Before actually making the payment, I would also check the mortgage contract. Prepayment privileges are lender- and contract-specific. The Financial Consumer Agency of Canada explains mortgage prepayment privileges and penalties as well as the different ways homeowners may be able to pay a mortgage off faster. A mathematically attractive $25,000 prepayment becomes less attractive if the lender is going to charge a penalty for making it.

My actual decision process would therefore start with the mortgage rate and the time remaining until renewal, then identify what the TFSA money would actually be invested in and calculate the expected spread. A one-point expected advantage over the mortgage is not enough to excite me. Two points becomes interesting. Three points over a long horizon starts becoming persuasive.

Then I would stop looking at the $25,000 and look at everything around it. Do I have enough liquid money? Am I already heavily concentrated in my house? Do I already have a large investment portfolio? How close am I to retirement? Would removing debt materially reduce the amount of income the household needs every month? If I invest the money, will it actually stay invested? If I pay down the mortgage, will I preserve the benefit, or will I simply find another way to increase consumption?

That is ultimately where I land on this question. Mortgage prepayment offers something rare: a nearly guaranteed improvement to the household’s financial position equal to the borrowing cost that disappears. TFSA investing offers something different: liquidity, diversification and the possibility of substantially greater long-term wealth. At low mortgage rates and long horizons, the expected investment advantage can become enormous. At high mortgage rates, debt reduction becomes one of the most competitive low-risk uses of capital available to a Canadian homeowner.

Between those extremes, I would focus less on whether the expected investment return is technically higher than the mortgage rate and more on how much higher it is. If my mortgage costs 5%, I am not taking equity risk because I hope to earn 6%. At 7%, I start paying attention. At 8%, with twenty years ahead of me, the investment case becomes much stronger. If the mortgage itself costs 6.5% or 7%, that hurdle rises dramatically.

None of those percentages matter, though, if sending the money against the house leaves the family without sufficient liquid capital. The best use of the next $25,000 is not automatically the option with the highest expected terminal value. It is the option that improves the household’s overall position when return, risk, liquidity, diversification, debt exposure and future flexibility are considered together.

Sometimes that means filling the TFSA. Sometimes it means making a very satisfying lump-sum mortgage payment. The useful part is knowing why.