Mortgage Payoff Calculator

There are only four levers, and they trade off against each other in ways the marketing around this topic tends to blur.

Add extra principal each month. The most flexible option and the one with no cost. You can stop any month, and every dollar goes straight at the balance. Nothing gets locked in.

Pay biweekly. Half your payment every two weeks is 26 half-payments a year, which is 13 full payments instead of 12. It’s the same as adding one-twelfth of a payment monthly, and you can do it yourself for free — servicers charging a setup fee plus a per-debit fee for the official program are charging you for automation, not for math.

Make a lump sum against principal. A bonus, an inheritance, proceeds from a sale. The earlier it lands, the more it does — a dollar in year one erases three decades of future interest on that dollar, and a dollar in year twenty-five erases almost none.

Refinance into a shorter term. A 15-year rate typically runs below a 30-year, so this is the only lever that improves your rate as well as your timeline. It’s also the only one that commits you: the higher payment becomes mandatory, and you pay closing costs to get there.

The first three are reversible. The fourth isn’t. If you’re not certain the higher payment survives a job change, the extra-principal route reaches the same payoff date with none of the commitment and none of the closing costs.

Where your extra payment actually goes

Servicers don’t all treat extra money the same way. Some apply it to next month’s payment, some park it in suspense, some prepay escrow — and any of those means you get none of the effect modelled above. Send it as a separate transaction marked apply to principal, then check next month’s statement that the balance actually dropped by what you sent.

* How the return figure works

It’s total interest saved divided by total extra paid — so 80% means every extra dollar spared you 80 cents of interest across the whole loan. It is not an annual rate. Spread over the years it took, the annualised equivalent is roughly your mortgage rate, and that’s the number to hold against an investment return, not the headline percentage.

If you’re still paying PMI

Prepaying has a second payoff here. Reaching 80% loan-to-value lets you request PMI cancellation, and dropping that premium is an immediate monthly saving on top of the interest. If you’re near that line, the first stretch of extra payments is worth noticeably more than the calculator above shows — it prices the interest, not the insurance you stop paying.

Prepay vs recast

They answer different questions. Prepaying buys time — the loan finishes sooner but the required payment never moves. A recast buys cash flow — the servicer re-amortizes a smaller balance over your remaining term, cutting the payment while keeping the payoff date. Same money, opposite outcome.

There’s no correct number, but there is a useful way to pick one.

Start with what you can sustain without touching your emergency fund, because the value of extra payments comes from consistency and the worst outcome is prepaying for two years then drawing it back out on a credit card at 22%.

Then check three thresholds. One-twelfth of your payment replicates the biweekly effect, roughly one extra payment a year, and typically takes four to six years off a 30-year loan. Enough to reach 80% LTV is worth targeting on its own if you’re paying PMI, because cancelling the premium is an immediate monthly saving on top of the interest. And whatever gets you to a round payoff year — some people find “done in 20” more motivating than an abstract interest figure, and motivation is what makes this work over decades.

Run each in the calculator above. The difference between $100 and $200 a month is usually larger than people guess, and the difference between starting now and starting in three years usually larger still.

Biweekly payments aren’t magic. Paying half your payment every two weeks is 26 half-payments a year — 13 full payments instead of 12 — and that one extra payment goes entirely to principal. Turn on biweekly in the calculator above to see what it does to your loan.

The free version. Divide your monthly payment by 12 and add that to every monthly payment as extra principal. It’s the same math, needs no special program, and your servicer accepts extra principal any time. An automatic transfer makes it stick.

The servicer’s program. Many servicers charge a setup fee plus a fee on every debit, then hold the half-payments and apply the extra once a year. It’s the same result as the free version, minus the fees — worth it only if forced automation matters more to you than the cost.

Prepaying earns you a guaranteed return equal to your mortgage rate. That’s the whole financial case, and whether it’s a good deal depends entirely on what that rate is.

Against a 7% mortgage, a guaranteed 7% return with no market risk is genuinely hard to beat. Against a 3% mortgage taken in 2021, it’s a poor trade — you’re retiring cheap debt you will never be offered again, and the same money in a savings account has recently paid more than that with full liquidity.

Three things generally come first regardless of the rate. High-interest debt, because a 22% credit card beats any mortgage rate on the board. An employer 401(k) match, because that’s an immediate return no mortgage rate approaches. And a real emergency fund, because home equity is the worst kind of illiquid — a paid-ahead mortgage does nothing for you if income stops, and you can’t ask for last year’s extra payments back.

There’s also a non-financial answer that’s worth taking seriously. Some people sleep better without a mortgage, and that has value even when the spreadsheet says invest instead. Just make it a choice you’ve priced rather than a rule you inherited.