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Formula
M = P × r(1 + r)^n ÷ ((1 + r)^n − 1); each month: Interest = Balance × r, Principal = M + Extra − Interest, new Balance = Balance − Principal
- M
- the scheduled monthly payment of principal and interest
- P
- the loan amount
- r
- the monthly interest rate, the annual rate ÷ 12 as a decimal (6% → 0.005)
- n
- the number of monthly payments in the original term
- Extra
- the optional extra amount paid toward principal every month
What the amortization calculator shows
Enter the loan amount, annual interest rate and term, and the amortization calculator returns the fixed monthly payment of principal and interest, the number of payments, the total interest and the total of all payments. Below the result you get the schedule itself, in one of two views:
- Month by month. One row per payment, with the amount paid, the part that went to principal, the part that went to interest, and the balance left afterward.
- Yearly summary. Principal and interest paid in each year of the loan and the balance at the end of that year.
Add an amount in Extra payment each month and the calculator re-runs the schedule with that extra going to principal from the first payment. It then reports the new payoff time, the total interest with extra payments, the interest saved and the time saved.
It works for any fixed-rate, fully amortizing loan: a mortgage, car loan, student loan or personal loan. For a home purchase that starts from the price and down payment, the mortgage calculator adds property tax and insurance; for a car, the auto loan calculator handles sales tax and trade-ins.
How to calculate an amortization schedule by hand
Take a $150,000 loan at 6% for 30 years (360 payments).
- Monthly rate: r = 0.06 ÷ 12 = 0.005.
- Growth factor: (1 + r)^360 = 1.005^360 ≈ 6.0226.
- Payment: M = 150,000 × 0.005 × 6.0226 ÷ 5.0226 ≈ $899.33.
- Month 1 interest: $150,000 × 0.005 = $750.00. Principal: $899.33 − $750.00 = $149.33. New balance: $149,850.67.
- Month 2 interest: $149,850.67 × 0.005 = $749.25. Principal: $150.08. And so on.
Over 360 payments the interest adds up to $173,757.28, more than the amount borrowed. The schedule is just steps 4 and 5 repeated until the balance reaches zero, which is exactly what the calculator does, at full precision.
Amortization calculator with extra payments
Extra principal payments work because every dollar off the balance stops earning interest for the rest of the loan. These figures are for a $200,000 loan at 6.5% over 30 years, with a scheduled payment of $1,264.14, and the extra paid every month from the start:
| Extra each month | Paid off after | Total interest | Interest saved | Time saved |
|---|---|---|---|---|
| $0 | 360 months | $255,088.98 | — | — |
| $100 | 293 months | $199,143.21 | $55,945.77 | 67 months |
| $200 | 250 months | $165,012.20 | $90,076.78 | 110 months |
| $500 | 177 months | $110,940.53 | $144,148.44 | 183 months |
The first $100 a month does the most work per dollar; each additional dollar still saves interest, just a little less. Before paying extra, check that your loan has no prepayment penalty — the CFPB notes that this depends on your contract and state law — and tell your servicer to apply the extra to principal rather than to next month’s payment.
How term changes the schedule
The same $200,000 at 6.5% over different terms:
| Term | Monthly payment | Total interest | Interest in year 1 | Principal in year 1 |
|---|---|---|---|---|
| 10 years | $2,270.96 | $72,515.15 | $12,567.66 | $14,683.85 |
| 15 years | $1,742.21 | $113,598.65 | $12,760.14 | $8,146.43 |
| 20 years | $1,491.15 | $157,875.11 | $12,851.54 | $5,042.21 |
| 30 years | $1,264.14 | $255,088.98 | $12,934.18 | $2,235.45 |
Year-1 interest barely changes with the term, because it depends mainly on the starting balance. What changes is how much principal you repay. On the 30-year loan only $2,235.45 of the first year’s $15,169.63 in payments reduces the debt.
Reading the schedule
Two patterns are worth knowing. First, the balance falls slowly at the start and quickly at the end. On the 30-year loan above, the balance after 10 years is still $169,552.25; it takes until payment 233, almost 20 years in, before more of each payment goes to principal than to interest. Second, that shape is why refinancing, selling or paying extra early has such a large effect: early in the loan, most of what you pay is interest. The guide to how loan amortization works walks through this in more detail.
Common mistakes
- Entering the APR when you know the note rate. The schedule is built from the interest rate. An APR that includes fees overstates the payment slightly.
- Comparing loans on payment alone. A longer term lowers the payment but raises total interest.
- Assuming extra payments go to principal automatically. Some servicers apply them to future payments unless you say otherwise.
- Expecting escrow in the payment. Taxes and insurance collected by a mortgage servicer are on top of the principal-and-interest payment shown here.
Glossary
- Amortization. Paying off a debt in regular installments that cover interest and part of the principal.
- Principal. The amount borrowed, or the part of it still owed.
- Amortization schedule. The table of every payment, split into principal and interest, with the remaining balance.
- Prepayment. Paying more than the scheduled amount, or paying the loan off early.
- Recast. Recalculating the payment on a lower balance while keeping the original rate and end date.
Worked examples
A 30-year home loan
$285,000 borrowed at 6.75% for 30 years, shown as a yearly summary.
Inputs: Loan amount = $285000; Annual interest rate = 6.75 %; Loan term = 30; Term unit = Years; Extra payment each month = $0; Schedule table = Yearly summary
r = 6.75% ÷ 12; n = 360 M = $285,000.00 × r(1 + r)^360 ÷ ((1 + r)^360 − 1) = $1,848.50 Month 1: interest $1,603.13, principal $245.38, balance $284,754.62
Answer: Borrowing $285,000.00 at 6.75% over 360 months: $1,848.50/month, $380,461.65 total interest.
A 15-year loan with $200 extra a month
$180,000 at 5.875% over 15 years, paying $200 more than the scheduled payment every month.
Inputs: Loan amount = $180000; Annual interest rate = 5.875 %; Loan term = 15; Term unit = Years; Extra payment each month = $200; Schedule table = Month by month
r = 5.875% ÷ 12; n = 180 M = $180,000.00 × r(1 + r)^180 ÷ ((1 + r)^180 − 1) = $1,506.81 Month 1: interest $881.25, principal $625.56, balance $179,374.44
Answer: Borrowing $180,000.00 at 5.875% over 180 months: $1,506.81/month, $91,226.39 total interest. Paying $200.00 extra a month clears it in 149 months and saves $17,393.30 of interest.
A short 0% loan
$4,800 at 0% interest repaid over 18 months, so every payment is principal.
Inputs: Loan amount = $4800; Annual interest rate = 0 %; Loan term = 18; Term unit = Months; Extra payment each month = $0; Schedule table = Month by month
r = 0% ÷ 12; n = 18 M = $4,800.00 × r(1 + r)^18 ÷ ((1 + r)^18 − 1) = $266.67 Month 1: interest $0.00, principal $266.67, balance $4,533.33
Answer: Borrowing $4,800.00 at 0% over 18 months: $266.67/month, $0.00 total interest.
Assumptions and limitations
- The interest rate is fixed for the whole loan and interest is charged monthly at the annual rate ÷ 12 on the balance at the start of each month.
- Payments are monthly, start one month after the loan begins, and are not rounded to the cent. The last payment is whatever clears the remaining balance, so lender schedules can differ by a few cents.
- Any extra payment is applied in full to principal every month from the first payment onward. The scheduled payment does not change; the loan simply ends sooner.
- Property tax, insurance, PMI, fees and prepayment penalties are not included. Check your contract to see whether extra payments are allowed and how they are applied.
- The term must be a whole number of months, up to 600 months (50 years).
Frequently asked questions
What is an amortization calculator?
It works out the fixed payment on a loan and then splits every payment into interest and principal, showing the balance left after each one. The result is an amortization schedule, which lets you see how slowly or quickly a loan is being paid down.
How do you calculate an amortization schedule?
Find the monthly payment with M = P × r(1 + r)^n ÷ ((1 + r)^n − 1). Then, for each month, multiply the opening balance by the monthly rate to get the interest, subtract that from the payment to get the principal, and subtract the principal from the balance. Repeat until the balance reaches zero.
How much do extra payments save?
It depends on the rate, the term and how early you start. On $200,000 at 6.5% over 30 years, paying $200 a month extra from the start pays the loan off 110 months (9 years, 2 months) sooner and saves $90,076.78 of interest, assuming the lender applies the extra to principal.
Why does my balance go down so slowly at first?
Interest is charged on the balance still owed, which is largest at the start. On a 30-year loan at 6.5%, about 85% of the first year's payments is interest, and principal does not overtake interest until payment 233.
Does an extra payment lower my monthly payment?
Usually not. On a standard fixed-rate loan the scheduled payment stays the same and the loan ends sooner. Some lenders will recast a mortgage after a large lump-sum payment, which lowers the payment, but that is a separate request and may carry a fee.
Can I download the schedule?
The table can be copied straight from the page into a spreadsheet, and the Copy result button gives a one-line summary. Switch the Schedule table option between month by month and yearly summary to get the view you need.
How do I calculate amortization on a loan with 0% interest?
With no interest, every payment is principal, so the payment is the loan amount divided by the number of months and the balance falls by the same amount each month.
Sources
- What is amortization and how could it affect my auto loan? — Consumer Financial Protection Bureau. Checked October 10, 2026.
- Can I prepay my loan at any time without penalty? — Consumer Financial Protection Bureau. Checked October 10, 2026.
- What is the difference between a loan interest rate and the APR? — Consumer Financial Protection Bureau. Checked October 10, 2026.