Amortization Calculator
Generate a full payment-by-payment amortization schedule for any fixed-rate loan. See how each payment splits between principal and interest, the running balance, and the impact of extra payments.
How to Use
- Enter the loan amount in dollars (the principal you actually borrow, not the home or asset price).
- Enter the annual interest rate (APR) as a percentage.
- Enter the loan term in years — common values are 5, 10, 15, 20, and 30.
- Optionally add an extra monthly principal payment to see how much faster the loan pays off.
- Toggle between yearly and monthly view to see either a high-level summary or every single payment.
- Each row shows: payment number, scheduled payment, interest portion, principal portion, extra principal, and remaining balance.
Formulas
History of Amortization
The word "amortize" comes from the medieval French amortir, "to deaden" — a debt that's gradually killed off through scheduled payments. The mathematics of level-payment loans, where each payment is identical but the principal/interest split changes over time, is essentially the same annuity formula used by Fibonacci in his 1202 Liber Abaci and formalized by Leonhard Euler in the 18th century. What was missing for centuries was the institutional scaffolding to apply it at scale to ordinary borrowers.
Before the 1930s, U.S. home loans were typically 5- to 10-year balloon notes: borrowers paid only interest each month, then owed the entire principal at the end. When the Depression made refinancing impossible, hundreds of thousands of those balloons defaulted simultaneously. The Home Owners' Loan Corporation in 1933 and the Federal Housing Administration in 1934 mandated long-term, fully-amortizing, fixed-rate loans as a structural fix, and the 30-year amortizing mortgage became the post-war American default.
Today amortization schedules are produced for every loan automatically by lender software, and Form 1098 reports each year's interest payments to the IRS using the same calculation. The math hasn't changed since Euler; only the spreadsheets and the regulatory framework around it have.
About This Calculator
This calculator generates the full amortization schedule for any fixed-rate, fully-amortizing loan: mortgage, auto, student, personal, business. It computes the level monthly payment from the standard annuity formula, then walks the schedule month by month, splitting each payment into interest (calculated against the previous balance) and principal (the remainder). Extra principal payments are applied at the start of each month and shorten the term.
The annual view collapses 12 months into one row showing total interest, total principal, and end-of-year balance — useful for tax planning and high-level reviews. The monthly view shows every payment for full transparency. Everything runs entirely in your browser; no balance, rate, or income information is transmitted or stored. For variable-rate loans, the schedule is only valid until the next rate reset.
Frequently Asked Questions
Why is the early payment mostly interest?
Interest each period is calculated against the remaining balance, which is at its maximum at the start of the loan. Even though your monthly payment is fixed, the interest portion is the highest in the first month and shrinks every period after as the balance drops. Principal payments do the opposite — they're tiny at first and grow over time.
How are extra payments applied?
Extra payments are typically applied directly to principal, reducing the balance interest is calculated against in subsequent months. Most U.S. mortgages allow this without prepayment penalty. Confirm with your lender — some auto-loans and consumer loans treat extra payments as advance payments rather than principal reductions, which doesn't actually save interest.
What's the difference between an amortization schedule and a loan?
The loan is the contract; the schedule is the payment plan. Two loans with identical principal, rate, and term will have identical schedules. The schedule visualizes what's happening under the hood: the same fixed payment every month, but with the principal/interest split shifting over time.
Does this work for car loans, student loans, and personal loans?
Yes — fully-amortizing fixed-rate loans of any kind use the same math. Just enter the principal, the APR, and the term. Variable-rate loans (some HELOCs, ARM mortgages, certain student loans) need the schedule recomputed each time the rate changes.
How is interest calculated each month?
Monthly interest = remaining balance × (annual rate / 12). For a $200,000 balance at 6.5% APR, the first month's interest is 200,000 × 0.0054167 = $1,083.33. The total payment minus this interest is the principal that month. Next month the balance is slightly lower, so the interest is slightly lower, and the principal portion is slightly higher.
What does 'fully amortizing' mean?
A fully-amortizing loan has each payment large enough to cover all interest accrued plus some principal, such that by the final payment the balance reaches exactly zero. The opposite is an interest-only or balloon loan, where some or all of the principal is still owed at the end of the term.
Common Use Cases
Mortgage payoff planning
See exactly how much faster a 30-year mortgage pays off with an extra $200/month vs. the scheduled payment alone.
Student loan strategy
Compare standard 10-year repayment vs. 25-year extended repayment to see lifetime interest cost.
Auto loan vs. cash decision
Generate the schedule to see total interest paid over the life of the loan, then decide whether financing or paying cash makes sense.
Refinance analysis
Compare your current loan's remaining schedule against a new loan's schedule at a lower rate to find the actual interest savings, then weigh against closing costs.
Round-up payment strategy
Test the impact of rounding your monthly payment up to the nearest $50 or $100 — small extras compound into years off the term.
Tax planning
Look up how much interest you'll pay in a given year for tax-deduction purposes (mortgage interest deduction, etc.). The schedule's annual view is exactly what your lender's Form 1098 will show.
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