Late-payment interest
calculator.
Calculate by day count or actual dates, including multiple payments toward principal and a detailed calculation trail.
Editable before calculation
Simple interest = outstanding principal × annual rate × overdue days ÷ 365. The divisor is always 365, including leap years. Interest for each period is rounded to two decimal places before totaling. Each payment reduces principal only; accrued interest is shown separately and does not earn interest. The 15% rate is an editable example default. Check the actual contract terms.
Enter the terms
Interest periods
Apply payment to principal at the end of each period, then use the remaining principal for the next period.
Outstanding balance
Enter the details and select Calculate
Results will appear here
Before using these results
This tool uses the assumptions above to help check amounts under the terms you enter. Verify the rate and agreement in the actual documents before using the result. Entries are processed only in this browser; customer data is not automatically stored or sent.