Quick guide
How to use this calculator
- Enter every amount in one consistent currency.
- Enter the rate convention and whole-number period requested by each label.
- Review the result together with the calculator-specific assumptions and exclusions.
Calculation method
Calculation method
Monthly interest equals the opening balance multiplied by the entered nominal annual rate divided by 12.
The calculation retains full floating-point precision internally and rounds only for display. Amortization advances one payment period at a time so principal, interest, extra payments, and the final payment remain explicit.
Worked example
Practical example
Calculate interest included in payments 1 through 60.
Monthly interest equals the opening balance multiplied by the entered nominal annual rate divided by 12.
Supported inputs
Precision and limits
Visible input limits
Numeric tokens accept at most 60 characters. Amounts are capped at 1e12, annual rates at 1000%, and mortgage schedules at 100 years or 1,200 monthly payments.
Estimate, not an offer
Results model only the entered values. A lender may use different day counts, payment timing, fees, rounding, qualification rules, or contractual allocation.
International scope
No currency, country, tax system, insurance rule, mortgage program, or lender policy is assumed. Location-dependent amounts must be entered explicitly.
Calculator-specific assumptions
Payment numbers are inclusive and must remain within the original mortgage term.