A loan payment looks flat for decades, and its insides shift every month. This calculator lays out the full schedule: how each payment splits between interest and principal, when principal finally takes over, and what the loan really costs by the end.
Every fixed-rate loan has one monthly payment that never changes. What changes, quietly and relentlessly, is what that payment is made of. In month one of a $320,000 mortgage at 6.95%, interest eats $1,853.33 of the $2,118.23 payment and principal gets the leftover $264.90. The lender is charging rent on nearly the entire loan, and the rent comes due before any of your money touches the debt itself.
From there the composition migrates. Each principal dollar slightly lowers the balance, each lower balance slightly lowers the interest charge, and the freed-up margin goes back to principal. The pace is brutal at the start. Ten years of payments on the default loan retire just $45,724.22 of principal, 14.3% of what you borrowed. Twenty years in, the figure reaches $137,158.74, still under half the loan. The first 180 payments generate $297,682.67 of interest while the final 180 generate $144,881.32, close to a two-to-one tilt toward the early years.
On these defaults, principal overtakes interest on payment 241, about twenty years into the loan. Half the term passes before the payment starts working mostly for you. Anyone budgeting around the idea that a five-year-old mortgage has built real equity should run this schedule first.
The default rate comes from the Freddie Mac Primary Mortgage Market Survey, the weekly benchmark for conforming 30-year loans. In the September 17, 2026 release, the 30-year fixed averaged 6.95%, up from 6.76% one week earlier and 6.26% a year before that. The 15-year fixed averaged 6.26%. Your own quote will move with your credit score, down payment, and points, so treat these as honest placeholders rather than offers.
Variables in plain terms. P is the loan amount. i is the monthly interest rate, the annual rate divided by 12, so 6.95% becomes 0.5792% per month. n is the total number of payments, 360 on a 30-year loan. The first equation prices the payment so the balance lands exactly on zero at payment n. The next three split every payment and track the balance down to it.
P is $320,000, i is 0.0695/12 = 0.005792, n is 360. The payment formula gives M = $2,118.23. Month one charges interest of 320,000 × 0.005792 = $1,853.33, so principal is $264.90 and the balance falls to $319,735.10. Month two charges interest on that smaller balance, $1,851.80, and principal rises to $266.43. That handoff repeats 358 more times, with principal growing every single month, until the final payment of $2,118.23 is $2,110.50 principal and $7.73 interest. Across all 360 payments the loan costs $762,563.99, of which $442,563.99 is interest, 58.0% of everything paid and 138.3% of the amount borrowed.
Two levers move every line of the table, the rate and the term. The rows below hold the $320,000 loan fixed and vary one at a time.
| Scenario | Monthly payment | Total interest | Principal overtakes interest |
|---|---|---|---|
| 30 years at 6.95% (default) | $2,118.23 | $442,563.99 | Payment 241 |
| 30 years at 7.45% (+0.5%) | $2,226.54 | $481,554.62 | Payment 250 |
| 30 years at 6.45% (−0.5%) | $2,012.11 | $404,358.43 | Payment 232 |
| 15 years at 6.95% | $2,867.31 | $196,116.28 | Payment 61 |
| 15 years at 6.26% (PMMS 15-year) | $2,745.50 | $174,189.56 | Payment 48 |
Read the rate rows first. Half a point on a $320,000 mortgage swings total interest by roughly $38,000 to $39,000 in either direction, which is why shopping two or three lenders is worth an afternoon. Then read the term rows. Moving to 15 years raises the payment by $749.08 and cuts interest by $246,447.71, and it moves the crossover from year 20 to year 5. The payment for that speed is real, so stress-test it against your take-home pay before committing.
The table this calculator prints is the same document your servicer keeps, so it answers concrete questions. Selling in year six? The balance row tells you the payoff figure before you request a quote, which feeds directly into the rent vs buy calculator if the decision is still open. Considering prepayments? Every extra dollar lands on the balance line and compounds in your favor, and the mortgage payoff calculator quantifies exactly how many years and dollars each extra amount saves. And if you want the payment itself for a different loan shape, the loan payment calculator prices any fixed-rate loan in one step and shows when principal finally overtakes interest, with this page supplying the anatomy behind it. Rates move after you close, too: the refinance break-even calculator applies the same balance-and-payment logic to the question of whether a cheaper rate justifies its own closing costs, given how long you expect to keep the loan.
One caution the schedule makes obvious. Home equity built in the first decade is mostly a mirage of timing, since interest has absorbed most of each payment. Anyone planning to tap that equity, or counting on it for a future down payment, should read the actual balance row for their sale year rather than the years-of-payments intuition.
Amortization is the fixed schedule that retires a loan with equal payments. Each payment first covers the interest the balance accrued that month, and whatever remains reduces the principal. Because the interest charge shrinks as the balance falls, an ever-larger slice of the same payment goes to principal, and the balance hits exactly zero on the final payment. The word describes the schedule itself, which is why lenders hand you an amortization table at closing.
On a $320,000 loan at 6.95% over 30 years, that crossover arrives on payment 241, roughly 20 years in. It depends entirely on the rate and the term. A 15-year version of the same loan crosses in month 61, and a short auto loan crosses almost immediately: on $30,000 at 7.5% over 5 years, the very first payment is mostly principal.
Interest is charged on the outstanding balance, and in year one that balance is nearly the full loan. A $320,000 mortgage at 6.95% accrues $1,853.33 of interest in month one, which consumes 87.5% of a $2,118.23 payment. Ten years of payments retire only 14.3% of the original balance, because interest is front-loaded onto the years when you owe the most.
Yes, dramatically. An extra dollar paid toward principal never accrues interest again, so it permanently shrinks the base that every later interest charge is computed on. Your required monthly payment stays the same and the loan simply ends years sooner with far less total interest. The exception is a formal recast, where the lender re-amortizes the remaining balance into a lower required payment over the original term.
The math is identical. What changes is the term, and the term decides where the crossover lands. A $30,000 auto loan at 7.5% over five years has a monthly payment of $601.14 and total interest of $6,068.31, and its first payment already puts more toward principal than interest. Long mortgages pay mostly interest early; short loans never get the chance to.
Use the actual rate on your loan quote or statement, which will differ from any national average based on your credit profile, down payment, and whether you paid points. The default here uses the Freddie Mac Primary Mortgage Market Survey 30-year average of 6.95% from September 17, 2026 as a realistic placeholder. Taxes and insurance escrow are excluded; the schedule covers principal and interest only.
All calculation logic on this page is implemented from the primary documents below. Each one is listed with the figure it supplies, so any rate or threshold in the result can be traced back to its published source.
Same published formulas, same sourcing standard, one page each.