The easiest way to calculate loan interest is with a calculator or spreadsheet. You’ll get a quick answer detailing interest costs over time, and you can add all the costs together to see what a loan’s total interest cost is. The following pages will help you get an answer without doing much math.
- Loan Amortization Calculator - shows how much interest is in each payment
- Excel Mortgage Calculation Tips - build a spreadsheet showing interest costs
Calculate Loan Interest Costs Yourself
If you do the math yourself, you’ll get a better feel for how a loan works. The best way to understand interest costs is to build an amortization table. You’ll calculate loan interest as a piece of every payment, and you can see how much interest you’ll pay over time.
Assume you borrow $100,000 at 6% for 30 years to be repaid monthly. How much interest will you pay? A sample amortization schedule (showing only the first few payments) appears at the bottom of this page. Total interest paid over the first 3 payments is $1,498.50 ($500 + $499.50 + $499).
Credit Card Interest
Credit card interest calculations are more difficult. With a credit card, your card issuer may use one of several different methods to calculate your interest charges. These calculations account for purchases and payments that occur throughout the month, and the card issuer’s approach to generating profits. For a description of these methods, see 6 Ways Finance Charges Are Calculated.
Calculate Loan Interest Rates
If you want to calculate a loan’s interest rate - as opposed to interest costs - see How to Calculate Interest Rates.
Sample Amortization Table
|Period||Starting Balance||Payment||Periodic Interest||Principal||Remaining Balance|