Loan calculator

How to calculate a loan payment

1. Select the loan type tab (auto, personal, or student).
2. Enter the loan amount and the annual interest rate.
3. Enter the term in months or years.
4. Review the monthly payment, total interest, and principal-vs-interest split.

Common uses

• Comparing car finance offers: enter each offer's amount, rate and term, and compare the total interest as well as the monthly payment.
• Choosing a term: lengthen or shorten the term, in months or years, and watch the principal-versus-interest bar shift as the total interest rises or falls.
• Checking affordability: turn your pay into a monthly figure to set against the payment, or estimate a home loan payment with tax and insurance for a larger purchase.

The finance tools guide compares the five finance calculators and the formulas behind them.

Technical specification

• Algorithm or formula: Standard amortization: M = P · [r(1+r)^n] / [(1+r)^n − 1], where P is principal, r is the monthly interest rate (annual / 12), and n is the number of months. Total interest = M · n − P. This is the level-payment (annuity) formula for a fully amortizing loan; see Kellison, The Theory of Interest (3rd ed., McGraw-Hill/Irwin, 2009), on annuities and amortization schedules.
• Browser API or library: Pure JavaScript arithmetic. The payment is computed as P · r / (1 − (1+r)^−n) with Math.log1p and Math.expm1, which keeps very high rates from overflowing. No external library.
• Input limits: Any positive principal and a rate of 0% or more; a result too large to calculate shows a note instead of figures. Term 1–600 months (50 years), entered in months or years; the term is rounded to whole monthly payments, and switching the unit converts the value in the box.
• Output: Monthly payment, total interest, total cost, and a principal-vs-interest visual breakdown.
• Known limitations: Models a fixed-rate, fully-amortising loan only. Origination fees, variable rates, extra payments, and balloon terms are not modelled; compare APR for fee-heavy loans.

Frequently asked questions

How is a loan payment calculated?

Monthly payments follow the amortization formula M = P[r(1+r)^n] / [(1+r)^n - 1], where P is the loan amount, r is the monthly interest rate, and n is the number of months. Each payment is split between principal and interest, with the principal share growing over time.

What loan types does this calculator handle?

The same amortization math powers auto loans, personal loans, and student loans. Switch the tab at the top of the calculator to set a sensible default term for each type.

Does the calculator account for fees?

Only the headline interest rate is modelled here. For a loan with origination or processing fees, compare the APR rather than the interest rate, since APR rolls most fees into the effective annual cost.

Is my loan information sent to a server?

All math runs in your browser as JavaScript. Our servers are not involved at any point.