Amortization Calculator

How a payment splits, month by month

The payment on a fixed-rate mortgage never changes, but its composition changes every single month. Interest is charged on the outstanding balance, so as the balance falls the interest portion shrinks and the principal portion grows by exactly the same amount.

The crossover point, and why it lands so late

Most people assume the split reaches even somewhere around the middle of the loan. On this one it does not happen until month 237 — year 19.8.

Over the whole of year one, $26,709 goes to interest and $4,296 to principal. That is 13.9% of the year's payments actually reducing what you owe. After twelve months of paying $2,584 you have moved the balance from $400,000 to $395,704.

The lateness of the crossover is a function of the rate, not of anything unusual about this loan. The higher the rate relative to the term, the later it falls; at a very low rate it arrives much earlier. It is the single most useful thing an amortisation schedule reveals, because it explains several things that otherwise look strange:

• ·Why selling early feels like you have paid nothing off. Five years in, the balance is $375,336 — you have retired 6% of the loan after paying $155,000.
• ·Why refinancing resets more than the rate. A new 30-year loan puts you back at month one of this curve, at the interest-heavy end, even if the rate is lower.
• ·Why extra principal early is so powerful. A dollar paid in month one cancels interest for 359 months. The same dollar in month 300 cancels it for sixty.

The Freddie Mac Primary Mortgage Market Survey rate used here is a weekly national average — 6.71% for the 30-year in the week ending September 3, 2026, mirrored by the Federal Reserve Bank of St. Louis. Your own schedule shifts with your rate, but its shape does not.

What changes the shape of the curve

Three inputs move an amortisation schedule, and they do not move it in the same way. Understanding which does what is most of the value of running one.

The term

Shortening the term is the most dramatic change, because it alters the balance of the very first payment. The same $400,000 at the PMMS 15-year average of 6.04% carries a payment of $3,384 and total interest of $209,134 — against $530,156 over thirty years. The 15-year borrower pays $800 more a month and $321,022 less in interest, and their crossover point arrives almost immediately rather than in year twenty.

The rate

The rate changes both the payment and the curvature. A higher rate pushes the crossover later, because more of every early payment is consumed by interest. This is why the same loan structure feels very different in a high-rate market than a low-rate one: not just the payment, but the pace at which you build equity.

Extra principal

Extra payments do not change the payment or the rate — they change the balance the interest is charged on, which pulls the whole schedule forward. Because interest is calculated on the balance each month, a single early extra payment removes interest from every remaining month at once. Our early mortgage payoff calculator prices that directly, and the biweekly payment calculator prices the specific version where the extra amounts to one payment a year.

What does NOT change the schedule is paying early within the month. A fixed-rate mortgage accrues on a monthly cycle, so paying on the 1st rather than the 15th does not reduce interest. Only additional principal does.

What the schedule does not include

An amortisation schedule covers principal and interest only. Your actual payment is usually larger, and the difference is not small.

• ·Property taxes and homeowners insurance. Escrowed monthly on most loans, and they rise over time while your principal and interest does not.
• ·Mortgage insurance. Required on most conventional loans below 20% equity. Note that IRS Publication 936 states the itemised deduction for mortgage insurance premiums has expired — it is a cost with no offsetting tax benefit.
• ·HOA dues. Never part of the mortgage, frequently part of the monthly reality.
• ·Escrow adjustments. Your servicer recalculates the escrow portion annually, so the total payment changes even though the amortised part does not.

On the tax side, the same publication allows the interest deduction on the first $750,000 of acquisition debt ($375,000 married filing separately), with a $1,000,000 limit grandfathered for debt incurred before December 16, 2017. Since the interest column above is front-loaded, the deduction is worth most in the early years — for the shrinking share of filers who itemise at all.

Reading your own schedule

Lenders are required to make an amortisation schedule available, and most servicers publish one in the online account. It is worth pulling once, early, and comparing it against what you expected.

Two things to check. First, that the payment splits the way the schedule says — if your servicer is applying part of the payment somewhere unexpected, this is where it shows. Second, the balance at the point you expect to sell or refinance, because that is the number that determines your proceeds, not the balance at the end of the term.

If the balance at your likely exit looks uncomfortably high, that is not a reason to distrust the schedule. It is the schedule doing its job: telling you, in advance, what an amortising loan actually does with your money in its early years.