15 Year Mortgage Calculator

The cleanest way to understand a 15-year term is to hold everything constant except the term and the rate it earns you. Here is the $350,000 example from the introduction, side by side — every figure below is reproducible in the calculator on this page:

Two things drive the gap. First, interest has half as many years to accrue. Second, each 15-year payment retires principal far faster, so every subsequent month's interest is charged on a smaller balance. Notice the five-year row: the shorter term has already cleared $83,469 of principal while the 30-year loan has cleared only $21,618 — nearly a 4-to-1 difference, from a payment that is only about 32% larger. For the full year-by-year table behind these figures, see our dedicated 15-year mortgage amortization schedule page, and its 30-year counterpart for the longer term. If the 30-year side of this table is where you are leaning, run your own loan amount and rate through the 30 year mortgage calculator, which adds payment-by-loan-amount tables and the balance you would still owe after 5 and 10 years.

The calculator uses the standard fixed-rate amortization formula:

M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]

where P is the amount borrowed, r is the monthly interest rate (annual rate divided by 12), and n is the number of monthly payments — 180 for a 15-year term. Plugging in the example above: P = $350,000, r = 0.061 ÷ 12 ≈ 0.0050833, n = 180. The formula returns $2,972.44, and multiplying by 180 payments gives $535,039 paid in total, of which $185,039 is interest. You can verify each step in the calculator on this page, or read the full derivation on our how mortgage amortization is calculated guide.

One caution when budgeting: this figure is principal and interest only. Property taxes, homeowners insurance, and any PMI ride on top of it, and on a 15-year loan the base payment is already high enough that those add-ons deserve explicit modeling. The calculator on this page has optional fields for property tax, insurance, HOA dues and a PMI rate, and our amortization calculator with taxes and insurance walks through the full monthly housing cost in more depth.

Fifteen-year loans don't just save interest through the shorter clock — they usually carry a lower rate in the first place. In Freddie Mac’s survey for the week of October 8, 2026, the 15-year fixed averaged 6.73% against 7.40% for the 30-year, a gap of 0.67 percentage points, and the calculator on this page opens at that 15-year average. Lenders price them cheaper because the money is at risk for half as long, prepayment behavior is more predictable, and borrowers who qualify for the higher payment tend to be lower credit risks. You can see the live spread between the two terms in Freddie Mac's weekly Primary Mortgage Market Survey, which publishes both averages every Thursday.

The spread compounds the savings. In the example above, only part of the $278,000 interest gap comes from the shorter term itself — the rest comes from the 0.6-point rate discount applied to every dollar of the balance for every month it's outstanding. When you compare terms in the calculator, always use a realistically lower rate for the 15-year scenario rather than the same rate for both; using identical rates understates the shorter term's advantage.

The catch is that lenders qualify you on the actual required payment. Each loan program caps total debt-to-income (DTI): for loans sold to Fannie Mae, the limit is 36% when manually underwritten, up to 45% with qualifying credit scores and reserves, and 50% through Desktop Underwriter (Fannie Mae Selling Guide B3-6-02, read October 12, 2026). On our $350,000 example, the 15-year payment of $2,972 (before taxes and insurance) demands roughly $715 more monthly income headroom than the 30-year alternative — and once you add escrow items, the qualifying payment might approach $3,700. At a 45% DTI ceiling with no other debts, that implies needing around $8,200 in gross monthly income versus roughly $6,600 for the 30-year version of the same house.

This is why the 15-year term fits some borrowers cleanly and disqualifies others from the same purchase price. It tends to suit: refinancers who have already built equity and income since their original loan; buyers well below their maximum budget; and borrowers within 10-20 years of retirement who want the mortgage gone before the paychecks stop. It fits poorly when the payment would crowd out emergency savings or retirement contributions — a locked-in obligation is very different from a goal you can pause.

A practical way to test the fit: run the 15-year payment through the calculator, add your estimated taxes and insurance, and check that the total, with your other debts included, stays inside the debt-to-income limit your loan program applies. If it only works when every other line of your budget goes perfectly, the shorter term is probably ahead of your finances rather than matched to them — and the synthetic-15 approach in the next section gets you most of the benefit without the contractual commitment.

The strongest case against the 15-year loan deserves a fair hearing. Take the 30-year loan, invest the $714 monthly difference, and if your investments return more after tax than your mortgage rate costs, you come out ahead — with the flexibility to stop investing during a rough year, which a contractual payment never allows. Over long horizons, diversified equity returns have often exceeded mortgage rates, though with real volatility and no guarantee over any particular 15-year window. The honest framing: the 15-year loan is a guaranteed return equal to your loan rate; investing the difference is a higher expected but uncertain return. Risk tolerance and discipline — whether the difference actually gets invested every month — decide which is right, and neither choice is irrational.

There's also a middle path the calculator models directly: keep the 30-year loan for its flexibility, but send extra principal as if it were a 15. Paying $3,087 a month on the 30-year loan at 6.7% retires it in exactly 15 years with about $205,748 in total interest — more than the true 15-year loan's $185,039, because you keep the higher 30-year rate, but $257,000 less than paying the 30-year loan on schedule. The premium buys an escape hatch: any month you need to, you can drop back to the required $2,258. Model your own version of this with the mortgage calculator with extra payments.

Every dollar figure above was generated with the same amortization formula the calculator uses — M = P × [r(1+r)ⁿ]/[(1+r)ⁿ − 1] — applied at 6.1% over 180 months and 6.7% over 360 months on a $350,000 principal, then cross-checked by summing the resulting payment schedules. The 6.1% and 6.7% rates are illustrative inputs, not quotes; the calculator itself opens at Freddie Mac’s 15-year average of 6.73% for the week of October 8, 2026. Your quoted rates will differ, which is exactly why the mortgage amortization calculator homepage and the tool on this page accept your own inputs rather than assuming ours. Rate history for both terms is published weekly by Freddie Mac. Nothing on this page is financial advice — it's arithmetic, presented so you can weigh a real trade-off with real numbers.