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Should you pay off your mortgage early, or invest the extra money?

It's one of the most argued-over questions in personal finance, and the pure-math answer is simple to state: if your expected investment return is higher than your mortgage's interest rate, investing the extra money usually wins on paper. If your mortgage rate is higher, or you'd rather not carry the risk, paying it down wins. Most online calculators stop there — they run a single dollar-for-dollar comparison and call it a day.

This calculator goes a step further in three ways. First, it runs the actual amortization math for whatever split you choose — not a rule of thumb — recalculating how many years it takes to pay off the mortgage at each allocation, and what your invested balance would be by the time the mortgage would've paid itself off anyway. Second, it asks you for your expected return risk-adjusted. Paying your mortgage down earns its rate guaranteed, while the market guarantees nothing, so a risky 7% isn't worth the same as a certain 6.5%. Economists call the rate you'd accept as a sure thing a certainty equivalent — enter that, rather than the optimistic headline number, and the comparison is honest before it starts. Third, a peace of mind cost handles the human side: being debt-free has value beyond the math, and you decide what that's worth.

There's a fourth thing most comparisons miss entirely, and it usually matters more than any of the above: what happens to your mortgage payment after the mortgage is gone. Paying extra doesn't only save interest — it ends the payment early. From the payoff date onward, the scheduled payment and the extra you'd been throwing at the loan are both free, and this calculator redirects every dollar of that into investments for the remaining years of the analysis. On a $2,500 payment with $1,000 extra, an allocation that clears the mortgage fifteen years early doesn't just free up $1,000 a month — it frees up $3,500 a month, with fifteen years left to compound. Calculators that ignore this quietly penalize early payoff and make investing look far better than it is.

Because your total monthly outflow stays identical across every split, mortgage interest isn't subtracted as a separate line item — it's already accounted for. Interest you don't pay is money that goes into the portfolio instead, starting the day you would have paid it, and the growth math values it at whatever it compounds to by the end. Deducting it again would double-count it. Every scenario spends the same amount, ends with the mortgage fully paid off, and differs only in what the portfolio grew to along the way. Run honestly, the gap between the extremes is usually a lot narrower than either camp claims.

To use it: enter your mortgage balance, interest rate, and current payment (from your mortgage statement), plus how much extra you have available each month to put toward either extra mortgage payments or investing. Set your expected return, already risk-adjusted — the rate you'd genuinely accept as a guarantee. Then set your peace of mind cost: the annual return you'd willingly give up for each year you still owe on the house. It's charged only while the mortgage exists and stops the day it's paid off, and it's expressed in the same units as the return right above it, so you can answer it by comparison — "I'd take 6% instead of 7% to be done fifteen years sooner." Set it to zero to see the pure-dollar answer. Then drag the allocation slider from all-investing to all-payoff and watch both lines move. The chart shows the whole curve at once, so you can see exactly where the dollar-optimal point sits relative to where you'd actually want to be.

Frequently asked questions

Should I pay off my mortgage early or invest?
It depends on your mortgage rate, your expected investment return, and how much being debt-free is worth to you personally. If your mortgage rate is low and you expect stocks or other investments to outperform it over time, investing the extra money tends to build more wealth on paper. But that's only the dollar answer, and it assumes a risky return is worth the same as a guaranteed one. This calculator lets you adjust for both: the risk you're taking to earn that return, and the real, non-financial value of paying off debt sooner. There's no single right answer that applies to every household.
How should I set the peace of mind cost?
It's a rate, in the same units as your expected return, which makes it answerable by comparison: if your return is 7%, would you accept 6% in exchange for being mortgage-free fifteen years sooner? If so, enter 1%. The cost applies only while the mortgage exists and stops at payoff, so there's no penalty that follows you around afterward. Start at zero, see the pure-dollar answer, then raise it until the recommendation changes. The number where it flips is the real output: that's how much being debt-free would have to be worth before it's your best move. Note that it flips fast when your return and your mortgage rate are close — a narrow dollar gap doesn't take much to overturn.
What return should I enter, and why risk-adjusted?
Paying down your mortgage earns exactly your mortgage rate, guaranteed. Investing might earn 7% on average, but it might also be down 30% in the year you need the money. Those aren't equivalent, and comparing them at face value overstates the case for investing. The fix is to enter your return as its certainty equivalent — the guaranteed rate you'd accept instead of the risky one. If you'd expect 7% from the market but would happily take a guaranteed 5.5%, enter 5.5%. There's no universal haircut; 1–2% off your headline expectation is a common starting point. It matters most when your mortgage rate is already close to your expected return, where it can flip the answer outright.
What happens to my mortgage payment once the loan is paid off?
All of it goes into investments, and the calculator models that explicitly. Once the mortgage is cleared, you stop owing the scheduled payment and you stop making extra payments toward it, so your entire monthly budget is free. If your payment is $2,500 and you'd been adding $1,000 on top, that's $3,500 a month flowing into the portfolio from the payoff date until the end of the analysis — and the earlier the payoff, the longer that money compounds. This is the single biggest reason aggressive payoff is more competitive than simple comparisons suggest. A calculator that only reinvests the extra $1,000 and lets the $2,500 vanish will understate every early-payoff scenario.
Why isn't mortgage interest subtracted from the final portfolio value?
Because it's already in the number. Every split spends the same total each month over the same horizon, and that money goes to exactly one of two places: the mortgage or the portfolio. A dollar of interest you avoid is a dollar that lands in the portfolio instead — and it lands there early, so it compounds for the rest of the analysis. That makes avoided interest worth considerably more than its face value. Subtracting total interest on top of that would count the same dollars against you twice and make early payoff look worse than it is. The mortgage rate still drives the whole comparison; it just does it through one channel instead of two.
Is it smarter to invest if my mortgage rate is low?
On pure dollar math, yes — a lower mortgage rate makes it easier for a diversified investment portfolio to out-earn what you'd save in interest by paying the mortgage down faster. That's why, with the peace of mind cost at zero and an unhaircut return, this calculator will usually show the highest value at or near 0% allocated to the mortgage. But notice how little it takes to flip that: when your expected return is only half a point above your mortgage rate, even a modest risk haircut erases the entire advantage. The wider the gap between the two rates, the more the dollars-only case survives scrutiny.
What's the difference between bi-weekly and semi-monthly mortgage payments?
Bi-weekly means a payment every two weeks — 26 payments a year, which works out to the equivalent of one extra full monthly payment annually, and meaningfully shortens a loan's payoff time. Semi-monthly means twice a month on fixed dates — 24 payments a year, the same total as paying monthly, just split in half. They're easy to mix up but they amortize differently, so check your mortgage statement for which one you actually have before running the numbers here.
Does paying off my mortgage early actually save money?
Yes — every extra dollar toward principal reduces the total interest you'll pay over the life of the loan, since interest is calculated on the remaining balance. This calculator shows that interest savings directly — it's baked into the portfolio figure, since interest you don't pay is money that gets invested instead. The open question isn't whether it saves interest — it does — but whether that guaranteed savings beats what the same money could have earned invested elsewhere instead.
Why doesn't the "best" allocation always match the highest portfolio value?
Because "best" means the highest value after your peace of mind cost. Every month you still carry a mortgage, that cost comes out of what actually gets invested, so scenarios that stay in debt longer lose ground even while the before-cost figure climbs. Set the cost to zero and the two lines meet everywhere. They also meet at 100% to the mortgage regardless of your setting — at that end you aren't investing anything during the payoff period, so there's nothing left to give up.
Is my mortgage and financial data stored anywhere?
No. Everything you enter is saved only in your browser's local storage — nothing is sent to a server, and there's no account or sign-in. That also means it's only available on this browser and device; use the dashboard's "Export all" button any time you want a backup file you can restore later or move to another device.