Monthly payment, total interest, and a simple amortization snapshot.
Enter principal, APR, term in years, and an optional extra monthly payment. The tool builds a fixed-rate amortizing schedule: base payment from the standard formula, then applies extra principal each month until the balance hits zero. You see the payment (base + extra), payoff time, total interest, total paid, interest saved vs paying the minimum, and a snapshot of the first 12 payments.
Works for any fixed-rate amortizing loan — auto, personal, student, or a simple mortgage PI view. Adjustable rates, deferred interest, and fees beyond APR are not modeled. For a full home payment with tax and insurance, use the mortgage calculator.
Extra payment goes to principal. It does not cut the rate. On a high APR, paying extra usually saves more interest than leaving the cash elsewhere at a lower return. On cheap debt, compare interest saved here to what you could earn investing the same cash. The first-12 table shows how early payments are interest-heavy — extra principal bites harder later, but starting early still shortens the whole schedule.
If the payment is too small to cover interest (common with a tiny payment on a high balance), the calculator errors instead of looping forever. Raise the payment or lower the rate/term inputs.
Extra payments keep your rate and shrink principal. A refinance changes the rate and usually adds closing costs. If you are deciding between throwing $200/mo at principal or paying fees for a lower rate, run this page and the refinance calculator with the same balance. Debt snowball/avalanche across several balances lives on debt payoff.
Set extra to $0 for the contractual schedule, then try $50 / $100 / $200 and read interest saved and months cut. Prefer the smallest extra you will actually sustain. Re-run when the APR quote or term changes — small APR swings move interest a lot on long terms.