About the Loan Interest Calculator

What is this tool?

The Loan Interest Calculator is a free web tool that works out the monthly payment and total interest for a loan amount, annual rate, and term. It supports:

• Three repayment methods: annuity, equal principal, and bullet
• An optional grace period (interest-only payments)
• A full payment schedule (payment number, payment, principal, interest, balance)
• A side-by-side total interest comparison for the same terms

How it calculates

Monthly interest is the remaining principal multiplied by the annual rate divided by 12. Amounts are rounded to whole units, and any rounding remainder is adjusted in the final payment. This matches the standard monthly method lenders use, but small differences can occur because each lender rounds sub-unit amounts and handles the first period's daily interest differently.

Why was it built?

Loan consultations usually quote only the monthly payment, which makes it hard to see how much the repayment method changes the total cost. Switching methods can move total interest by millions on a large loan. This site exists so you can line up all three methods under identical terms before you sign anything.

This is a reference tool, not financial advice or a lending decision. Confirm actual terms with your lender.