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. Loan amounts, rates, and terms are not transmitted.

Loan calculator

Loan calculator is a finance tool that works out monthly payments for auto, personal, and student loans using the standard amortization formula. It reports total interest, total cost, and a visual principal-versus-interest split, and accepts the term in months or years. The tool runs in your browser.

Loan type

Currency

Loan amount

Interest rate (% per year)

Term

Formula: M = P[r(1+r)^n] / [(1+r)^n - 1], where P = loan amount, r = monthly rate, n = months

Dedicated pages

Loan-specific calculators with pre-set defaults.

Auto Loan Calculator

Calculate monthly car loan payments, total interest, and total cost. Enter loan amount, annual interest rate, and term. Free, in-browser.

Personal Loan Calculator

Calculate monthly payments, total interest, and full cost of a personal loan. Free amortization calculator that runs in your browser.

Student Loan Calculator

Calculate monthly student loan payments, total interest, and total cost. Standard 10-year amortization, free, runs in your browser.

How to calculate a loan payment

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

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.
Browser API or library: Pure JavaScript arithmetic and Math.pow. No external library.
Input limits: Any positive principal and rate. Term in months or years; the toggle just multiplies by 12.
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. Loan amounts, rates, and terms are not transmitted.

Calculations are estimates for informational purposes only. Consult a financial professional for advice.

Reviewed and tested May 25, 2026.