Amortization Calculator
Generate a full amortization schedule for any loan, showing how each payment splits between principal and interest and how the balance falls month by month.
How to use the Amortization Calculator
- Enter your inputs into the Amortization Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The amortization mechanics
Interest_k = Balance_(k−1) · r · · · Principal_k = M − Interest_k · · · Balance_k = Balance_(k−1) − Principal_k
Each month, interest is charged on the current balance. Whatever is left of the fixed payment after interest reduces the principal. Early in a loan most of the payment is interest; by the end almost all of it is principal.
Worked example
On a $200,000 mortgage at 6.5% for 30 years, month 1: interest = 200,000 × 0.065/12 ≈ $1,083; principal = $1,264 − $1,083 = $181. By month 240, of the same $1,264 payment, about $688 goes to principal and $576 to interest.
Frequently asked questions
Why is so much of my early payment interest?
Because interest is charged on the outstanding balance, which is largest at the beginning of the loan. As the balance falls, the interest portion shrinks and the principal portion grows.
How do extra principal payments work?
Extra payments reduce the balance immediately, which lowers every future interest charge. Even small recurring extras can cut years off a long-term loan.
Are biweekly payments better than monthly?
Biweekly half-payments produce one extra full payment per year (26 half-payments = 13 monthly equivalents). That single extra payment can shorten a 30-year mortgage by 4–6 years.