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Interest calculator

Find out how much interest a loan costs per month and per year, and what it adds up to over the whole term.

Your numbers

Repayment

The same payment every month. The interest part shrinks over time.

Result

Interest the first year

$3,849

Put a second set of numbers beside this one and see the difference.

Interest the first month
$333
Total interest
$21,494
Payment the first month
$1,012

A loan of $100,000 at 4% costs $333 in interest the first month and $3,849 the first year. Over 10 years the interest comes to $21,494.

The interest rate is a nominal annual rate, charged monthly, and payments are made at the end of each month. Fees, interest deductions and changes in the rate are not included.

A month’s interest is the loan amount times the rate divided by twelve. A loan of 1 000 000 at 4 % costs 3 333 in interest the first month, and about 40 000 the first year if nothing is repaid. Repayments shrink the debt, so the interest falls over time.

Choose the repayment to match the loan: equal payments (an annuity) keep the payment the same every month, with the interest share falling and the principal share growing; equal principal repays the same amount every month and the payment falls; interest only never repays, so the interest is the same every month. The total over the term is what differs, and it is what the loan costs.

Last reviewed October 19, 2026 ·How pages are reviewed

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