An amortization schedule calculator that turns a loan amount, interest rate and term into a complete, payment-by-payment table. For every payment it shows how much goes to interest, how much reduces the principal, and the remaining balance afterwards, plus running totals for interest paid. It is built for anyone with a mortgage, car loan, student loan or personal loan who wants to see exactly where their money goes and how to clear the debt sooner.
How it works
The tool models a standard amortising loan: a fixed payment that fully repays the balance over the term. First it computes the level payment from the loan amount, the periodic interest rate (the annual rate divided by how many payments you make each year) and the total number of payments. Then it simulates each period in turn. It charges interest on the current balance, applies the payment, sends the remainder to principal, and rolls the lower balance forward to the next period. Because interest is always charged on what you still owe, early payments are mostly interest and later payments are mostly principal — the schedule makes that shift visible row by row.
On top of the base schedule you can model two kinds of overpayment. A recurring extra payment adds a fixed amount to every period, and a one-time lump sum lands on a payment number you choose — useful for a bonus, tax refund or inheritance. Both go entirely to principal. The calculator runs an untouched baseline in parallel so it can report the interest saved and the number of payments removed from the term. Switching the payment frequency between monthly, bi-weekly and weekly shows why more-frequent payments retire a loan faster: bi-weekly is 26 payments a year, the equivalent of an extra month of payments annually. A dual-axis chart plots the falling balance against the per-period principal/interest split, and Export CSV downloads every row.
Example
A $250,000 loan at 6.5% APR over 30 years, paid monthly, has a payment of about $1,580. Over the full term you pay roughly $319,000 in interest — more than the loan itself.
Now add a $200/month extra payment. The loan clears about 5 years and 8 months early and you save in the region of $77,000 in interest. Drop in a single $10,000 lump sum on payment 12 as well and the savings climb further, all visible instantly in the summary cards and chart.
| Loan | Rate | Term | Monthly payment | Total interest |
|---|---|---|---|---|
| $20,000 | 7.0% | 5y | $396 | $3,761 |
| $250,000 | 6.5% | 30y | $1,580 | $319,000 |
| $250,000 | 6.5% | 15y | $2,178 | $142,000 |
| $250,000 | 5.5% | 30y | $1,419 | $261,000 |
Every figure is calculated in your browser — no loan numbers are ever uploaded or stored.