The Cost of Certainty: Why Paying Off Debt Is Rarely Just Math
Few financial decisions feel as virtuous as paying off debt, and few are as misunderstood. The impulse is deeply Canadian and entirely understandable. We carry more debt than we ever have, roughly $1.80 for every dollar of disposable income at the start of 2026, and the idea of being free of it carries an almost moral weight.¹
That weight is precisely the problem, because it tempts us to treat what is really a series of judgments as a single arithmetic question. The instinct is to compare the interest rate on the debt to the return we might earn by investing, and to act on whichever number is larger. The arithmetic matters, but it can also be the smallest part of the decision.
Paying down debt is a trade-off with at least five moving parts: the interest rate set against the return you could reasonably expect, your preference for liquidity, your own psychological comfort, the tax-deductibility of the interest, and whether leverage is something you can use deliberately rather than something that simply happens to you. These rarely point in the same direction. For some people, eliminating debt reduces stress in a way no spread could justify. For others, preserving capital for investment is the more rational course. The work is not finding the universal answer. It is matching the decision to the person and to the whole balance sheet.
The Number Everyone Reaches For
The textbook rule is simple enough to be dangerous. If the after-tax cost of your debt is higher than the after-tax, after-fee return you expect from investing, pay down the debt. If the expected return is higher, invest. The rule is not wrong, but it simply hides the most important word in the comparison.
That word is guaranteed. Every dollar used to pay down debt earns a certain, risk-free, after-tax return equal to the interest rate you no longer pay. Investing offers an expected return, an average drawn across decades, with no promise about the years that actually matter to you. The two sides of the comparison are not the same kind of thing, and pretending like they are is how reasonable people end up disappointed.
The current Canadian backdrop sharpens the point. The Bank of Canada held its policy rate at 2.25% in June 2026, leaving the prime rate at 4.45%.² ³ The best available five-year fixed mortgages sit near 4.04% and variable rates near 3.35%, while home equity lines of credit are commonly priced around prime plus half a point, close to 5%.⁴ Against that, the 2026 Projection Assumption Guidelines that Canadian planners rely on call for nominal equity returns of roughly 6.3% for Canadian stocks, 6.4% for U.S. stocks, and 6.6% internationally, and those are gross figures, before investment fees of perhaps a percent and before any tax.⁵ Net the fees and the tax against a sub-four-percent mortgage and the supposed advantage of investing narrows to a thin, uncertain margin. At the other extreme, unsecured balances and credit cards near 20% are no contest at all. The mortgage is a genuine question; the credit card never is.
Why the Math Is Not the Whole Answer
An expected return is an average, and you do not get to live in the average. You live through a particular sequence of years, and a poor one early can do lasting damage even when the long-run number eventually arrives. The guaranteed return from retiring debt carries no such sequence risk. That asymmetry deserves more respect than a single percentage comparison gives it.
Then there is the part the spreadsheet cannot price, and the research here is more pointed than most people expect. A 2023 study of more than 3,700 adults found that it is the worry about debt, rather than the simple presence of debt, that most strongly predicts depressive symptoms and suicidal ideation. People who worried about debt showed markedly elevated risk, while debt unaccompanied by worry showed far weaker associations.⁶ This reframes psychological comfort from a soft consideration into a substantive one. For someone who lies awake over a balance, the return on peace of mind can genuinely exceed any spread the portfolio might earn, and a plan that ignores that is not a rigorous plan, it is an incomplete one.
The Tax Layer Most People Miss
In Canada, not all debt is taxed the same way, and the difference changes the math more than almost anything else. Under the Income Tax Act, interest is deductible when the borrowed money is used for the purpose of earning income from a business or property. Borrow to invest in assets that can produce dividends or interest, and the interest is generally deductible. Borrow to buy the home you live in, and it is not, because the home produces no income. The Canada Revenue Agency traces the use of the funds rather than the asset pledged as security, and the onus sits with the taxpayer to document that trail.⁷
The consequence is concrete. A non-deductible mortgage at 4.04% costs you the full 4.04%. A deductible investment loan at 5%, in the hands of someone at a 50% marginal rate, costs only 2.5% after the deduction. The deductible loan is far easier to clear with an expected return, while the non-deductible mortgage demands more from the portfolio than it first appears. This is why the order of operations is rarely about the headline rate alone. As a general rule, high-rate and non-deductible debt should be retired first, and low-rate, deductible debt last. It is also the logic behind strategies such as the Smith Manoeuvre, which gradually converts non-deductible mortgage interest into deductible investment-loan interest. The idea is sound, but it is not free of risk and it rewards discipline and the right balance sheet rather than enthusiasm.
Liquidity Is a Position, Not an Afterthought
A dollar used to prepay a mortgage is, for practical purposes, is gone. It sits behind a wall of home equity, reachable only by borrowing against the house again, on the lender's terms and timeline. Capital that stays invested or in reserve preserves something the prepaid dollar surrenders, which is optionality: the ability to meet an emergency, fund an opportunity, or absorb a stretch of lumpy income without being forced to act at the wrong moment.
For business owners and anyone with variable earnings, that access can matter more than the marginal interest a prepayment would save. None of this argues against paying down debt. It argues for sequencing, with an adequate emergency reserve established before either aggressive prepayment or aggressive investing, because liquidity is the position that lets every other decision be made deliberately rather than under pressure.
Leverage, Used Deliberately
For some households, preserving capital to invest is not a rationalization. It is the more rational path, particularly when the debt is cheap, deductible, and matched in term to a genuinely long horizon. Used this way, leverage is a deliberate decision rather than an accident of circumstance, and that distinction is everything.
Leverage amplifies outcomes in both directions, and it works only for a borrower who can withstand the downside without being forced to sell into it. Three risks deserve naming:
Rate risk falls on variable-rate debt, where the cost can rise faster than the strategy assumed.
Sequence risk falls on the portfolio, where an early loss is harder to recover when borrowed money is involved.
Behavioural risk falls on the borrower, because leverage that a household cannot emotionally sustain is leverage that gets unwound at precisely the wrong time, converting a paper loss into a permanent one. Leverage you cannot hold through a bad year is not really a strategy. It is exposure waiting to be regretted.
Can You Carry It, and Do You Need It?
Underneath every one of these tradeoffs sits a more basic question that no expected return can answer: what do the household's cash flows actually look like, and how much pressure can they take? Before comparing a mortgage rate to a projected return, it is worth mapping income stability, the monthly surplus that remains after fixed obligations, and how predictable that surplus really is. A decision to carry debt is also a commitment to make a payment every month, in good years and in bad. With many Canadian borrowers still moving through renewals, and with the Bank of Canada signalling that rates could move in either direction, the right test is not whether today's payment is comfortable but whether the household could sustain a materially higher one if a variable rate resets or a fixed term renews at a higher level. Debt that is affordable at 4% and unaffordable at 6% is less a financing decision than a bet on interest rates, and it deserves to be recognized as one.
The second question is quieter, and often skipped entirely: is the debt, or the leverage, actually required to reach the goal? If the financial plan already achieves its objectives without borrowing, then taking on leverage adds risk in pursuit of a return the household does not need. One of the few genuinely durable principles in planning is to avoid risks you are neither compensated for nor required to take. Leverage earns its place when the after-tax math and a long horizon clearly favour it, and it loses that place when it simply layers avoidable risk onto a plan that was already on track. This is also where capacity and willingness must be told apart. Personal risk tolerance describes how much volatility you are willing to live with; cash flow and serviceability describe how much you can actually withstand. The two are not the same, and a sound decision has to respect both.
Matching the Decision to the Person
Put the five tradeoffs together and they seldom resolve into a single clean answer, which is the honest conclusion rather than an evasive one. The right course depends on the rate and whether the interest is deductible, on how certain the alternative return really is, on the value you place on liquidity, on whether the household's cash flows can carry the payments through a stretch of higher rates, on whether the debt is even required to reach the goal, and on your own relationship with risk and with debt. Two households with nearly identical balance sheets can reach opposite conclusions and both be correct.
Reducing stress is a legitimate return, so is preserving capital. The discipline is not to default to a rule of thumb or to an emotion, but to decide deliberately, weighing the arithmetic against everything the arithmetic leaves out, and against the entire balance sheet rather than one line of it.
From Calculation to Decision
Debt decisions are not won on a spreadsheet. The arithmetic draws the boundaries of what is sensible, and within those boundaries the decision is a matter of judgment: about certainty, liquidity, temperament, and what a particular dollar is actually for in a particular life.
At Westmount Wealth Management, this is the kind of decision we are built to weigh. We evaluate every debt question across the entire balance sheet, considering the rate and its deductibility, the cash flow it touches, the liquidity it consumes, and the comfort of the people who have to live with it, and we coordinate with your other professionals, so the answer fits the plan. Certainty has both a price and a value. The task is to decide, in good time and with a clear head, how much of each you actually want to own.
References
1. Statistics Canada. “National Balance Sheet and Financial Flow Accounts, First Quarter 2026.” The Daily, June 12, 2026. https://www150.statcan.gc.ca/n1/daily-quotidien/260612/dq260612a-eng.htm.
2. Bank of Canada. “Bank of Canada Maintains the Policy Rate at 2¼%.” Press release, June 10, 2026. https://www.bankofcanada.ca/2026/06/fad-press-release-2026-06-10/.
3. Ratehub.ca. “Prime Rate in Canada.” Accessed June 19, 2026. https://www.ratehub.ca/prime-rate.
4. Ratehub.ca. “Compare Canada Mortgage Rates.” Accessed June 19, 2026. https://www.ratehub.ca/mortgages.
5. FP Canada and Institute of Financial Planning. “2026 Projection Assumption Guidelines.” FP Canada, 2026. https://www.fpcanada.ca/projection-assumption-guidelines.
6. Stickley, Andrew, Aya Shirama, and Tomiki Sumiyoshi. “Financial Debt, Worry about Debt and Mental Health in Japan.” BMC Psychiatry 23 (2023): 757. https://doi.org/10.1186/s12888-023-05235-4.
7. Canada Revenue Agency. “Income Tax Folio S3-F6-C1, Interest Deductibility.” Government of Canada. Accessed June 19, 2026. https://www.canada.ca/en/revenue-agency/services/tax/technical-information/income-tax/income-tax-folios-index/series-3-property-investments-savings-plans/series-3-property-investments-savings-plan-folio-6-interest/income-tax-folio-s3-f6-c1-interest-deductibility.html.
