You have an extra $300 a month. Your mortgage rate is 7%. Should you pay down the mortgage faster or put that $300 into an investment account? This is one of the most common financial questions homeowners ask, and unlike most financial dilemmas, it has a fairly clear answer — it just depends on one number.
If your mortgage rate is higher than your expected after-tax investment return, pay down the mortgage. If your expected after-tax return is higher than your mortgage rate, invest. Right now, with mortgage rates in the 6.5–7.5% range for most borrowers, this is genuinely a close call — closer than it has been in over a decade.
The Math Side of the Decision
A 7% mortgage rate means every extra dollar toward principal earns you a guaranteed 7% return — your balance goes down, the interest stops, and that money is freed. It's not 7% you might earn. It's 7% you definitely stop losing.
The S&P 500 has returned roughly 10% annually on average over long periods. But that's pre-tax, and it's an average that includes years of -30% returns alongside years of +25%. The realistic after-tax, inflation-adjusted return for a taxable investment account is closer to 6–7% — which puts it in direct competition with paying down a 7% mortgage.
| Scenario | Mortgage extra payment | Invest instead | Better choice |
|---|---|---|---|
| Mortgage at 4% (older loan) | Guaranteed 4% return | Expected 7%+ after tax | Invest |
| Mortgage at 6% | Guaranteed 6% return | Expected 6–7% after tax | Toss-up |
| Mortgage at 7% | Guaranteed 7% return | Expected 6–7% after tax | Lean toward mortgage |
| Mortgage at 7.5%+ | Guaranteed 7.5%+ return | Expected 6–7% after tax | Mortgage wins |
The mortgage interest deduction complicates this slightly — if you itemize, the effective rate of your mortgage is slightly lower than the stated rate. But since the 2017 tax law changes raised the standard deduction, fewer than 10% of taxpayers itemize, meaning most homeowners don't receive a meaningful deduction benefit.
What Extra Payments Actually Do to Your Timeline
On a $400,000 mortgage at 7% over 30 years, the monthly principal and interest payment is approximately $2,661. Total interest over the life of the loan: about $558,000.
Adding $300/month in extra principal payments from day one:
- Pays off the loan roughly 6 years and 4 months early
- Saves approximately $109,000 in total interest
- That $300/month, compounded over the removed 76 payments, is effectively earning a guaranteed 7% on every dollar
That $109,000 in saved interest is real, permanent, and risk-free. It doesn't depend on market conditions. The equivalent gain from investing $300/month at 7% for the same 6.3 years would be roughly $28,000 in additional portfolio value — which doesn't come close to the interest savings, because the mortgage savings are front-loaded and guaranteed.
When Investing Clearly Wins
If you have a mortgage from 2020 or 2021 at 3–4%, the math strongly favors investing. A guaranteed 3% return from extra mortgage payments versus an expected 7–10% from equities is not a close call — invest the money.
The same logic applies to tax-advantaged accounts. Contributing to a 401(k) up to your employer match is an immediate 50–100% return on that money. Contributing to a Roth IRA locks in tax-free growth for decades. Both of these beat extra mortgage payments at virtually any interest rate.
The order of operations most financial planners recommend:
- Emergency fund (3–6 months of expenses)
- 401(k) up to employer match
- High-interest debt (above 7–8%)
- Roth IRA to annual maximum
- Then: extra mortgage payments vs. additional investing based on rate comparison
The Non-Financial Case for Paying Off the Mortgage
A paid-off home provides something an investment portfolio doesn't: certainty of housing. If your income drops or you face an extended job loss, zero mortgage payment gives you options that a portfolio — which you'd need to sell from at a potentially bad time — doesn't. For people within 5–10 years of retirement, that certainty has real value that doesn't show up in the rate comparison.