How Personal Loan Interest Is Calculated

Quick answer: Many installment loan examples use a fixed-payment amortization formula where each payment covers interest and principal. Actual lender terms may vary.

Published: September 26, 2026 | Last updated: September 26, 2026 | Written by: Borrow Your Loan Editorial Team

Amortization basics

With a fixed installment loan, interest is commonly calculated from the remaining balance. Early payments often include more interest; later payments reduce more principal.

Formula used in examples

Estimated monthly payment = P x r / (1 - (1 + r)^-n), where P is principal, r is monthly interest rate, and n is number of monthly payments.

What examples exclude

Educational examples do not include lender-specific fees, optional products, payment timing differences, late payments, or state-specific rules.

Methodology

This page is educational and uses illustrative examples. Borrow Your Loan does not publish unverified partner rates, approval odds, or lender requirements. A lender or partner controls any final offer, APR, fee, amount, repayment term, and funding decision.

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