The math usually favors investing. But math isn't the whole story.
Your mortgage has a guaranteed cost: its interest rate. Every extra dollar you put toward it earns a guaranteed, risk-free return equal to that rate — because it reduces the interest you'd otherwise pay.
Investing has an expected return: historically around 7% per year in real terms (after inflation) for a diversified stock index fund. That's not guaranteed — it's a long-run average with significant year-to-year variation.
The logic is straightforward: if your mortgage rate is lower than your expected investment return, the math says invest. If your mortgage rate is higher, pay it off. The difficulty is that investment returns are uncertain while mortgage savings are not.
Here's how different mortgage rates stack up against the S&P 500's historical real return of roughly 7% per year:
| Mortgage rate | vs S&P 500 (~7% real) | Math says |
|---|---|---|
| 2–3% (old low-rate mortgage) | 7% investing return | Invest — clear winner |
| 4–5% | 7% investing return | Invest — probably |
| 6–7% | 7% investing return | Close call — either is fine |
| 7–8% | 7% investing return | Lean toward mortgage |
| 8%+ | 7% investing return | Pay off mortgage |
Take a $300,000 mortgage at 6.5% interest, 30-year term. You have $500/month to put somewhere. Here's how the two paths play out over 20 years:
At a 6.5% mortgage rate, investing wins by roughly $110,000 in this example — but only if markets deliver their historical average. In a decade where stocks return 3%, the mortgage payer would come out ahead.
Paying off your mortgage is one of the very few genuinely risk-free investments available to ordinary people. The return is exactly equal to your mortgage rate — no market risk, no volatility, no sequence-of-returns problem.
Investing is not guaranteed. The S&P 500 has delivered long-run averages of ~7% real, but individual decades have returned far less. The 2000s saw essentially zero real return over 10 years. If you're in a period like that, the mortgage payer wins.
Past returns don't guarantee future ones. The guaranteed return argument is real and shouldn't be dismissed just because the historical average favors investing.
The math gets more nuanced once you factor in taxes. In the US, mortgage interest may be tax-deductible if you itemize deductions — which effectively lowers your real mortgage rate. A 6.5% mortgage with a 22% marginal tax rate works out to roughly a 5% after-tax cost.
On the investing side, contributions to tax-advantaged accounts — 401k/IRA (US), RRSP/TFSA (Canada), ISA/pension (UK), super (Australia) — often reduce your taxable income today or enable tax-free growth, boosting your effective return on every dollar invested.
These factors can tilt the math — sometimes significantly — but they're secondary to the core rate comparison. If you're in the close-call zone, it's worth running the numbers with your actual tax situation.
Many people do both — and that's entirely reasonable. Make your regular mortgage payment, invest consistently into your retirement accounts, and periodically make lump-sum extra mortgage payments when you receive a bonus, inheritance, or other windfall.
This approach captures some of the guaranteed return of mortgage paydown, keeps your investments compounding, and avoids betting everything on one outcome. It's not the mathematically optimal answer for any specific rate scenario, but it's a sensible hedge against uncertainty.
The worst outcome isn't choosing the "wrong" side of this debate — it's being so paralyzed by the choice that you do nothing with the money. Both paths build wealth. Either is far better than leaving surplus cash idle.
It depends on your specific rate. If you locked in a mortgage at 2–3% years ago, investing still likely wins mathematically even in a higher-rate environment — because your guaranteed cost is still low. If you've recently taken out a mortgage at 7–8%, the case for overpaying is much stronger, since you'd need investments to consistently outperform that rate after tax to come out ahead.
As you approach retirement, the certainty argument for paying off the mortgage becomes more compelling. You'll have less time to recover from a bad sequence of investment returns, and a paid-off home dramatically reduces your monthly expenses in retirement.
Many people find the peace of mind of entering retirement debt-free worth more than the theoretical extra return from investing — and that's a completely valid trade-off, not just an emotional one.
Both benefit from extra payments, but a 30-year mortgage carries more total interest over its life, so extra payments save more in absolute terms. The rate matters more than the term: an extra payment on a 6.5% 30-year mortgage is a guaranteed 6.5% return. If that's higher than your expected investment return, prioritize the mortgage regardless of term length.
Generally not — unless the savings are truly excess beyond your emergency fund and other financial goals. Wiping out your liquid savings to pay off a mortgage leaves you with no financial buffer. A sudden job loss or large expense could force you into debt at much higher rates than your mortgage.
Keep your emergency fund (3–6 months of expenses in a HYSA) intact. Only use genuinely surplus funds — money you're confident you won't need — for extra mortgage payments.