Amortization Calculator

An amortization calculator splits every fixed loan payment into interest and principal: interest = balance × periodic rate, and the rest of the payment pays down the balance. For $250,000 at 6.5% over 30 years, the monthly payment is $1,580.17. Payment 1 is $1,354.17 interest and $226.00 principal, and total interest comes to $318,861.58.

How to use the amortization calculator

1. Enter the loan amount, the interest rate (APR) and the term in years or months.
2. Choose how often you pay: monthly, biweekly, weekly, or an accelerated biweekly or weekly plan. Set the date of the first payment so every row has a real date.
3. Optional: open Extra payments to add an amount to every payment, once a year, or as a one-time lump sum with a chosen payment number.
4. Read the schedule. Switch between every payment (with a subtotal after each calendar year) and a yearly summary, press Show all rows to see the whole table at once, or Copy as CSV and paste it into a spreadsheet.

Amortization formula

An amortized loan has a fixed payment that clears the balance exactly after the last payment. The payment is

Payment = P × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1)

• P is the amount borrowed.
• r is the rate per payment period: the APR as a decimal divided by the number of payments a year (12 for monthly, 26 for biweekly, 52 for weekly). 6.5% paid monthly gives r = 0.065 ÷ 12 ≈ 0.00541667.
• n is the total number of payments: years × payments per year. A 30-year monthly loan has n = 360.

Each row of the schedule then repeats three steps:

1. Interest = current balance × r, rounded to the cent.
2. Principal = payment − interest.
3. New balance = old balance − principal.

Because the payment is rounded to the cent, the last payment is usually a few cents different so the balance ends at exactly $0.00. On the example loan, the last payment is $1,580.55.

How to read an amortization schedule

Here are the first three payments and the last one for $250,000 at 6.5% for 30 years (r ≈ 0.00541667):

As the CFPB explains, at the beginning of an amortizing loan more of each payment generally goes to interest than to principal. On this loan, principal does not overtake interest until payment 233, more than 19 years in. Half of all the interest is paid by payment 127, and the balance does not fall below half the loan until payment 257.

Yearly amortization summary

Grouping the same loan by loan year (12 payments each) shows the shift from interest to principal:

The calculator’s yearly view groups by calendar year instead, so its first and last rows can hold fewer than 12 payments.

Monthly, biweekly and weekly payments

Paying more often only changes the schedule if the rate per period and the number of payments change with it. With biweekly payments, r = APR ÷ 26 and n = years × 26; with weekly payments, r = APR ÷ 52 and n = years × 52. For the example loan:

A true biweekly schedule saves only a few hundred dollars. The large saving comes from accelerated plans, which pay half the monthly payment every two weeks: 26 half-payments equal 13 monthly payments a year instead of 12. You get the same effect by adding one-twelfth of a payment to every monthly payment. Before signing up for a paid biweekly service, read the fees: in 2015 the CFPB sued one company that charged a setup fee of up to $995 plus yearly processing fees for this kind of program. Ask your lender first whether it accepts extra principal payments directly.

Biweekly and weekly dates follow a 14-day or 7-day cycle, so 26 payments take 364 days and the payoff date drifts slightly earlier than the term.

Extra payments and amortization

Extra money goes straight to principal, so every later interest charge is calculated on a smaller balance. On the example loan, an extra $200 each month clears the loan in 265 payments instead of 360 (7 years and 11 months sooner) and cuts total interest from $318,861.58 to $221,243.14, a saving of $97,618.44. A single lump sum also helps: on a $25,000 loan at 7.5% for 5 years ($500.95 a month), a one-time $10,000 with payment 12 ends the loan two years early and saves $2,503.42. Check whether your loan has a prepayment penalty, a fee some lenders charge if you pay off all or part of a mortgage early.

Common mistakes with amortization

• Using the yearly rate for r. Divide the APR by the number of payments a year.
• Assuming equal principal each month. The payment is fixed; the principal part grows every month.
• Calling standard biweekly payments “accelerated”. Only the half-the-monthly-payment version adds a 13th monthly payment each year.
• Comparing payments, not totals. A 15-year loan for the same $250,000 at 6.5% costs $2,177.77 a month but only $141,998.15 in interest.
• Forgetting escrow. A mortgage bill may include taxes and insurance, which are not part of the amortization schedule.

Results are estimates for a fixed-rate loan. Lenders that charge interest daily, round differently or add fees will show slightly different numbers. This is not financial advice.

Sources

• CFPB: What is amortization and how could it affect my auto loan?, checked November 2026
• CFPB: CFPB files suit against Nationwide Biweekly (May 11, 2015), checked November 2026
• CFPB: What is a prepayment penalty?, checked November 2026

Amortization practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

What is an amortization schedule?

It is a table with one row per payment showing the date, the payment, how much goes to interest and to principal, and the balance left. Running totals show how much interest you have paid so far.

How is each loan payment split between interest and principal?

Interest is the balance times the periodic rate; the rest of the payment is principal. On $250,000 at 6.5%, the first monthly interest is $250,000 × 0.065 ÷ 12 ≈ $1,354.17, so $226.00 of the $1,580.17 payment reduces the balance.

Why do I pay so much interest at the start of a loan?

Because interest is charged on the balance, and the balance is largest at the start. As it shrinks, the interest part of each payment falls and the principal part grows.

Do biweekly payments pay off a loan faster?

Only if they add up to more each year. Half the monthly payment every two weeks makes 13 monthly payments a year and cuts the example 30-year loan to about 24 years. A biweekly payment sized for 26 payments a year saves very little.

How do I make an amortization schedule in Excel or Google Sheets?

Use =PMT(rate/12, years*12, -amount) for the payment, then build rows with interest = previous balance × rate/12, principal = payment − interest and balance = previous balance − principal. Or press Copy as CSV above and paste the finished schedule.

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