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Is it better to pay off your house or invest the difference?
A mortgage is the cheapest money most people will ever borrow, which argues for keeping it. It is also a guaranteed return, which argues for killing it. Here is how the comparison actually resolves.
You have $1,000 a month spare and a mortgage. Send it to the lender and you are debt-free years early. Send it to the market and you might end up with more.
Both sides of this argument are usually made badly. One side compares a guaranteed return to an average one as though they were the same kind of number. The other treats a paid-off house as an emotional indulgence rather than a real financial position. Here is the version with the numbers in it.
What paying it down actually returns
Take a $300,000 balance at 6.5% over 30 years. Left alone, it costs about $382,633 in interest.
Add $1,000 a month to principal:
- Interest drops to about $141,471
- You save roughly $241,162
- The loan clears in 153 months instead of 360 — twelve and a half years early
The return on that $1,000 is exactly 6.5%, guaranteed, with no variance. Not expected. Not on average. Exactly.
It is also effectively tax-free, and that is the adjustment that most often gets missed. There is no tax on interest you did not pay.
Why the mortgage interest deduction usually does not save it
The standard counter-argument is that mortgage interest is deductible, so the real cost of the debt is lower than the rate.
That is true only if you itemize, and most households do not. For 2026 the standard deduction is $16,100 filing single and $32,200 married filing jointly. Mortgage interest has to clear that bar, together with your other itemized deductions, before a single dollar of it reduces your tax.
On a $300,000 balance at 6.5%, first-year interest is around $19,000. For a married couple that is well under the standard deduction on its own, so unless there are substantial other itemized deductions, the deduction is worth nothing at the margin and a 6.5% mortgage costs a full 6.5%.
Note too that the deduction only applies to acquisition debt — money used to buy, build or substantially improve the home — capped at $750,000 of balance for debt incurred after 15 December 2017.
The other side, fairly stated
Investing wins when the expected return, after tax, beats the mortgage rate by enough to compensate for the risk. Over long horizons, in a tax-advantaged account, that is a reasonable expectation at low mortgage rates.
And low really is low. A 3% mortgage is close to free money. Prepaying one to earn a guaranteed 3% while a tax-deferred account plausibly returns more is a poor trade, and the case for keeping it is strong.
At 6.5% or 7%, the same argument is much weaker. The guaranteed return is now in the range of what a diversified portfolio is expected to deliver before tax and before a bad decade.
The payoff house versus invest calculator runs both paths side by side, which makes the sensitivity visible: try it at a 4% assumed return and at a 9% one and see whether the answer flips.
What the spreadsheet cannot price
Liquidity runs against prepaying. Money in the house is unreachable without selling or borrowing against it, on that day's terms, subject to that day's approval. $100,000 in a brokerage account is $100,000 you can use.
Sequence risk runs against investing. A guaranteed 6.5% and an expected 6.5% are not the same thing. The expected one comes with the possibility of a bad first decade, and your payment schedule does not care how the market did.
A paid-off house lowers the floor. Your required monthly spending drops permanently, which changes what a job loss or an early retirement looks like. That is a real financial effect, not a feeling, even though it does not appear in a rate comparison.
The order that comes first
Before either option:
- Capture any employer retirement match in full. It is an immediate return that no mortgage rate approaches.
- Fund an emergency buffer. Prepaying a mortgage and then meeting a crisis with a credit card is refinancing 6.5% debt into 24% debt.
- Clear anything expensive. A car loan at 9% or a card at 22% outranks both options here.
After those, the comparison is real.
What to do with this
- Below about 4%, keeping the mortgage and investing is the stronger case over long horizons.
- Above about 7%, prepaying is hard to argue against — a guaranteed, tax-free 7% is an excellent asset.
- In between, run it at two different return assumptions. If the answer flips between them, you have learned that you do not know, and the certain option has a genuine claim.
- Consider splitting it. Half to the mortgage, half to the market, is not a failure to decide. It is a reasonable response to not knowing, and it captures some of each.
- Check whether a shorter term is the better tool. Refinancing into a 15-year loan gets much of the prepayment benefit at a lower rate, at the cost of committing to the higher payment rather than choosing it each month.
The argument gets heated because the middle band is genuinely close, and people defend the tiebreaker they actually care about — certainty or upside — as though it were the arithmetic.
Sources: IRS Publication 936, Home Mortgage Interest Deduction, for the acquisition-debt requirement and the $750,000 limit. Standard deduction figures read from the same constants the calculators use. Interest and payoff figures computed with this site's own amortization.