What an amortization schedule actually shows
An amortization schedule is the month-by-month receipt for paying off a loan. Every row is one payment. Each payment is the same dollar amount, but the schedule breaks it into two parts that change every month: the interest portion (which is large at the beginning) and the principal portion (which is small at the beginning). The schedule also shows the running balance, which falls a little more with each payment until it hits zero on the final row.
People rarely see this schedule before they sign for a mortgage, an auto loan, or a student loan. The lender quotes a monthly payment and a total cost, and most of us nod and sign. But the schedule is where the real story lives. It's the difference between knowing "I pay $1,896 a month for 30 years" and knowing "in year one, $19,500 of my $22,754 in payments goes straight to the bank as interest, and I'll own $3,254 more of my house."
The Amortization Calculator builds that schedule for any amortizing loan. Mortgage, auto, student, personal — anything with a fixed monthly payment and a fixed term. You enter three numbers and it does the rest.
How to use the Amortization Calculator
Three inputs, no signup, results update as you type.
- Enter the loan principal — the amount you actually borrowed. For a mortgage, that's the purchase price minus your down payment. For an auto loan, the financed amount on your contract.
- Enter the annual interest rate (APR). The calculator divides by 12 internally to get the monthly rate.
- Enter the term in years. A 30-year mortgage is 30. A 5-year auto loan is 5. The maximum is 60 years.
The headline shows your monthly payment, the total you'll pay over the life of the loan, and the total interest. The interest figure is usually the surprise — on a 30-year mortgage at current rates, you typically pay more in interest than you borrowed in the first place.
Below the headline you can toggle between the year-summary view (one row per year, fits on a screen) and the month-by-month view (every single payment, scrollable). The year view is best for seeing the shape of the loan. The month view is what you'd want in front of you in a meeting with a lender.
The formula behind the schedule
The monthly payment for an amortizing loan comes from a single equation. It looks intimidating but it does one thing: it picks the constant payment that, applied month after month, drives the balance to zero exactly at the end of the term.
M = P × [r(1 + r)^n] / [(1 + r)^n − 1]
M = monthly payment. P = principal. r = monthly interest rate (APR ÷ 12 ÷ 100). n = total number of months.
Once you have the monthly payment, building the schedule is just bookkeeping. For each month, compute interest on the current balance, subtract it from the payment to find the principal portion, and reduce the balance by that principal. Repeat.
Each month: interest = balance × r → principal = M − interest → new balance = balance − principal.
The reason the math works out to a zero balance at month n is precisely what the original formula is solving for. If you change the payment by even a dollar, you either finish with a small leftover balance or overpay by a small amount on the final row. The calculator handles this rounding correction so the last payment lands exactly at zero, the way real lenders do.
A worked example: $300,000 at 6.5% for 30 years
Let's run a realistic 2026 mortgage. You buy a $360,000 house, put down 60,000, and finance the remaining $300,000 at 6.5% for 30 years.
Plug in P = $300,000, r = 0.065 ÷ 12 ≈ 0.005417, n = 360. The formula gives a monthly payment of about $1,896.20. Over 30 years you'll pay 360 × $1,896.20 = $682,632 total, of which $382,632 is interest. You'll pay back more than twice what you borrowed.
Now look at where that money actually goes. The schedule shifts dramatically across the loan:
| Payment number | Interest portion | Principal portion | Remaining balance |
|---|---|---|---|
| Month 1 | $1,625.00 (85.7%) | $271.20 (14.3%) | $299,728.80 |
| Month 60 (year 5) | $1,512.66 | $383.54 | $278,946.13 |
| Month 180 (year 15) | $1,162.59 | $733.61 | $213,839.86 |
| Month 240 (year 20) | $901.85 | $994.35 | $165,461.97 |
| Month 360 (last) | $10.22 | $1,885.98 | $0.00 |
In month one, 86 cents of every dollar goes to the bank as interest. By the halfway point, the split is closer to 60/40. In the final year you're paying down the loan in big chunks of principal because the balance is small and the interest on it is small.
This is what people mean when they say "you don't really build equity for the first ten years." It's literally true. Year one of this mortgage adds about $3,300 to your owned share of the house. Year twenty-nine adds about $20,400.
Why early principal payments save so much money
Every interest charge in the schedule is calculated on the remaining balance. Lower the balance, lower every future interest charge. And because the same fixed monthly payment is split into interest plus principal, a smaller interest portion means a bigger principal portion — which lowers the balance even more — which lowers the next month's interest. The effect compounds in your favor.
On our $300,000 example: an extra $200 per month applied to principal cuts the total interest from $382,632 to about $245,000 and pays off the loan around seven and a half years early. That's roughly $137,000 saved on a $48,000 commitment of extra payments. The Amortization Calculator doesn't model extra payments — use the Mortgage Payoff Calculator for that — but knowing the structure of the schedule is what makes the savings feel real.
The same logic explains why people refinance when rates drop sharply. A lower rate at the start of a new schedule means more of every payment goes to principal from day one.
What the schedule does not include
Amortization is the math of paying off the loan itself. It does not cover the other costs that ride along with a real mortgage payment. If your monthly check to the lender is larger than the calculator says, those extras are the reason.
- Property tax — usually escrowed by the lender and paid on your behalf twice a year. Adds anywhere from $100 to $1,000+ per month depending on where you live.
- Homeowner's insurance — also typically escrowed. Roughly $100 to $300 per month for a median US home.
- PMI (private mortgage insurance) — required if you put less than 20% down on a conventional loan. About 0.3% to 1.5% of the loan amount per year, until you reach 20% equity.
- HOA dues — paid directly to a homeowner's association, not through the lender. Highly variable.
The four combined together are why "PITI" (principal, interest, taxes, insurance) is the relevant number for budgeting a home purchase. The amortization schedule is just the P and I.
For other loans the schedule is usually the whole picture. An auto loan payment is principal and interest only — no escrow. Same for most student loans and personal loans. The calculator gives you the full story for those.
Where this differs from other money calculators
An amortization schedule is for loans where each monthly payment is fixed and the loan pays off completely at the end. That covers most of what people borrow, but not everything.
- Payment Calculator — same formula, but solves for any of the three variables. Use it when you want to know the max loan you can take on given a target monthly payment, or how long it'll take to pay off at a given monthly amount.
- Mortgage Payoff Calculator — adds the extra-payment scenario. Models how much interest you save and how many months you shave off by paying more than the minimum.
- Simple Interest Calculator — for loans that don't amortize. Simple interest is interest charged only on the original principal, not on the running balance. Some short-term personal loans and certain car loans work this way.
- Savings Calculator — the mirror image. Compound interest working in your favor instead of against you.
Credit cards are not amortizing loans. They're revolving credit with no fixed end date, and minimum payments are calculated as a percentage of the balance, not a constant dollar amount. The amortization formula doesn't apply.
Frequently asked questions
What's amortization?
Amortization is the process of paying off a loan with regular fixed payments where each payment covers (a) interest on the current balance, plus (b) some principal that reduces the balance. The dollar amount of the payment stays the same, but the split between interest and principal shifts month by month. The schedule is the table that shows the shift.
Why is interest so high in the early years?
Interest is calculated each month on the remaining balance. In month one, the balance is the full loan amount, so interest is at its maximum. By the final month, the balance is near zero, so interest is near zero. On a $300,000 30-year mortgage at 6.5%, month one is 86% interest. The last month is 1% interest. The schedule walks you from one extreme to the other.
How is the final payment handled?
If you compute the schedule with exact floating-point math, the balance after 360 months usually lands at a tiny non-zero number — a fraction of a cent — because of rounding. Real lenders round each payment to the cent, accumulating small errors, and adjust the final payment slightly so the balance hits exactly zero. The Amortization Calculator does the same. The final row will usually be within a few cents of the regular payment.
Does this match what my lender sent me?
Within a few cents per month for the principal and interest portion. Lenders use slightly different rounding rules (some round to the nearest cent, some round up to the nearest dollar) and may include escrow items in the monthly figure they show you. The Amortization Calculator gives you pure principal and interest — the part of the payment that actually retires the loan.
What about an adjustable-rate mortgage?
This calculator assumes a fixed rate for the full term. ARMs recalculate the payment when the rate adjusts, so the schedule changes mid-loan. For an ARM, compute the schedule for the initial fixed period (often 5 or 10 years at the teaser rate), then assume the cap rate for the remainder as a worst case. Most ARM borrowers refinance before the adjustable period anyway, so the initial-period schedule is usually what matters.
What's the difference between amortization and depreciation?
Both are gradual processes that use similar math, but they apply to opposite sides of the balance sheet. Amortization is the schedule of paying off a debt — a loan balance going to zero. Depreciation is the schedule of writing down the value of an asset on accounting books — a value going to its salvage figure. Accountants sometimes use "amortization" for intangible assets (patents, software) and "depreciation" for physical ones (machinery, vehicles), but the underlying math is the same idea.
Can I see how extra payments would change this?
Not in the Amortization Calculator — it shows the schedule for the contract terms as written. For extra-payment scenarios, the Mortgage Payoff Calculator models exactly that: regular schedule versus accelerated schedule, side by side, with months saved and interest saved spelled out.
Does it work for international loans?
The math is universal — any amortizing loan with a fixed monthly payment uses this formula. But the conventions differ. UK mortgages often quote rates differently and may use daily-interest calculations. Some European loans pay quarterly or biannually. For a US-style monthly schedule, the calculator is exact. For other conventions, it'll be a close approximation but not penny-perfect with your local lender's quote.