Extra to Pay Off a 30-Year Mortgage in 15 Years

Cutting a 30-year mortgage down to 15 years is pure arithmetic, but almost every article tells you to "just pay extra" without saying how much. The honest answer: the extra you need is simply the difference between your 30-year principal-and-interest payment and what the same loan would cost on a true 15-year term. Pay that gap every month toward principal, and your payoff date moves to year 15. Below are illustrative numbers for common balances and rates, plus how to derive your figure in under a minute.

The short formula

Required extra per month = (15-year P&I payment on your balance and rate) minus (your current 30-year P&I payment). That single subtraction is the whole answer. The catch is that you need both payment figures, and they depend on three things: your remaining balance, your interest rate, and how many years are actually left. A freshly originated loan needs more extra than a "seasoned" loan you've already paid on for a few years, because the seasoned loan has less time and a smaller balance to compress.

Reference table: extra needed on a new 30-year loan

These figures assume a brand-new 30-year mortgage (full 360-month term remaining), principal and interest only, no taxes or insurance. The rates are illustrative, not current market quotes, and the dollar amounts are rounded. Plug your own numbers into the calculator below for an exact figure.

Two things jump out. First, a higher rate means a smaller dollar gap between the 30- and 15-year payments, but a far larger interest saving, because you are escaping more compounding. Second, the interest you avoid is enormous: tens to hundreds of thousands of dollars, often approaching or exceeding the loan principal itself.

Seasoned loans need less extra

If you are several years into your loan, you owe less and have fewer years to target. Suppose you borrowed $300,000 at 5.5% and have paid it down to a $250,000 balance. Your contractual P&I is still about $1,703. The 15-year payment on $250,000 at 5.5% is about $2,043, so you only need roughly $340 extra per month to clear the balance in 15 years from today. The lower your balance, the smaller the gap, which is why the same "pay it like a 15" goal gets cheaper the longer you have owned the home.

How to derive your exact number

Round numbers in a table will not match your loan to the dollar, and they ignore extras like PMI or escrow. Use the mortgage calculator with its extra-payment field to get your precise figure:

1. Enter your current loan: remaining balance, interest rate, and years remaining (use your real payoff term, not 30 if you have already paid for a while).
2. Note the baseline payoff date and total interest with no extra payment.
3. Type a trial extra-principal amount and watch the new payoff date. Start near the table figure for your balance and rate.
4. Nudge the extra up or down until the payoff date lands at 15 years. The total-interest line shows your savings versus the baseline.

This trial-and-error takes about a minute and accounts for your exact balance and rate. To compare against a formal 15-year refinance, the refinance break-even calculator shows whether a lower rate justifies the closing costs.

Biweekly payments: the same idea, smaller dose

You will see "switch to biweekly payments" pitched as a payoff trick. Paying half your monthly amount every two weeks produces 26 half-payments a year, which equals 13 full monthly payments instead of 12, so you make one extra payment annually. On a $300,000 loan at 6.5%, that is roughly $158 of extra principal per month and trims the term by about six years, not fifteen. Biweekly is a gentle accelerator; reaching a true 15-year payoff requires the larger extra from the table. If your servicer charges a fee to set up biweekly billing, skip it and just add the extra principal yourself.

Keep the 30-year, pay it like a 15

A 15-year refinance usually carries a lower rate, but it locks you into the higher payment. The flexible alternative is to keep your 30-year loan and voluntarily pay the 15-year amount each month. You get the same payoff timeline and nearly the same interest savings, but if you lose income, you can legally drop back to the lower required 30-year payment without penalty. You trade a slightly higher rate for an emergency-brake on your cash flow. Before committing the extra cash, make sure higher-return or higher-cost priorities come first; our guide on whether to pay off debt or invest walks through that tradeoff.

Gotchas before you start

• Mark it "apply to principal." Note the memo or use your servicer's extra-principal field, or the money may be parked as a prepaid future payment instead of reducing the balance.
• Check for a prepayment penalty. Most modern conforming loans have none, but confirm in your note.
• Don't starve your emergency fund or employer 401(k) match to do this. The match is a guaranteed return a mortgage payoff cannot beat.
• Verify the math, not the marketing. Recasting and refinancing are different levers; see recast vs. refinance if you would rather formally lower your payment.

These figures are estimates for planning, not personalized financial advice. Confirm your loan's terms with your servicer, and for general guidance on prepayment and penalties, the Consumer Financial Protection Bureau (CFPB) at consumerfinance.gov is a reliable, unbiased source.

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