Should you pay off a 3.5% mortgage or invest?
With a 3.5% mortgage and a 7% expected investment return, investing the extra money ends roughly $138,052 ahead after 30 years. But that's only the math on averages — paying off a mortgage is a guaranteed return and buys real peace of mind.
Why the mortgage rate decides it
Paying off a mortgage is a guaranteed return equal to the mortgage rate. Investing is an expected return with risk. So the comparison is simply 3.5% guaranteed vs ~7% (risky) expected:
- When the mortgage rate is well below your expected return (like 3.5% vs 7%), investing usually wins on average — your money compounds faster than the loan costs.
- When the mortgage rate approaches or exceeds your expected return, paying it off wins — and it's a certain win, with no market risk.
- Guaranteed vs risky matters. A paid-off house lowers your fixed costs and sequence-of-returns risk in retirement. Many people rationally choose the guaranteed return even when investing edges it out on paper.
Before you decide
A few things this comparison assumes you've already handled: capturing your full 401(k) match (an instant ~100% return that beats both), paying off any high-interest debt (credit cards dwarf a mortgage rate), and keeping an emergency fund. Money locked in home equity is hard to access without a sale or a HELOC — so don't pay down the mortgage with money you might need.
Assumptions: $450k home, 20% down, 30-yr term, an extra $12,000/yr toward principal, 7% investment return, 3% inflation, single filer. Mortgage interest is only deductible if you itemize — most people take the standard deduction, so this treats it as non-deductible. Model your own numbers in the calculator.
A cheap fixed rate is quietly an inflation hedge
A fixed-rate mortgage is one of the few debts that gets cheaper over time without you doing anything. The payment is frozen in nominal dollars, so as prices and incomes drift upward over the years, you repay the balance in dollars worth steadily less than the ones you borrowed. At a low fixed rate, inflation quietly does much of the work of shrinking the loan for you.
Prepaying retires that hedge early. When you can borrow long at a rate near the bottom of the range, keeping the mortgage and letting inflation erode its real weight is itself a defensible strategy — you hold onto cheap, long-dated, fixed financing that is hard to replace once you give it up.
Two conditions matter. The protection applies only to a fixed rate; an adjustable loan can reset higher and offers none of it. And this reasoning sits behind the basics, not ahead of them — capture the match, clear high-interest debt, and fund an emergency reserve before deciding what to do with the rest.
Common questions
Should I pay off a 3.5% mortgage or invest?
On average, investing wins by about $138,052 over 30 years because a 7% expected return beats the 3.5% guaranteed by paying it off. But paying off is guaranteed and risk-free, which many people rationally prefer.
Is it worth paying off my mortgage early?
Financially it's worth it when your mortgage rate is at or above your expected after-tax investment return. Below that, investing usually builds more wealth — though a paid-off home reduces risk and fixed costs, which has real value beyond the math.
What should I do before paying extra on my mortgage?
Capture your full 401(k) match, clear high-interest debt (credit cards), and hold an emergency fund first — each of those beats extra mortgage payments. Only then does paying down a low-rate mortgage compete with investing.