THE NUMORIX GUIDE
How to use the Repayment Calculator
Last reviewed September 14, 2026
What this calculator does
The engine converts the nominal annual rate using the selected compounding frequency, then converts that effective annual rate to the selected payment frequency.
Formula and method
The engine converts the nominal annual rate using the selected compounding frequency, then converts that effective annual rate to the selected payment frequency. Fixed-time mode calculates the installment over years and additional months; fixed-installment mode solves the number of payment periods with a logarithmic formula. Total payments are payment amount times the period count, and total interest is total payments minus starting balance.
Variables and inputs
Enter loan balance, annual interest rate, compound frequency, payback frequency, and Fixed Time or Fixed Installment mode. Fixed Time needs years and months; Fixed Installment needs a payment amount. Frequency choices range from yearly to daily, with compounding also offering a 365.25-period option.
Worked example
For a $25,000 balance at 6%, monthly compounding and monthly payment over 5 years, the converted monthly rate is 0.06 / 12 = 0.005 and the period count is 60. The installment is 25000 x 0.005 x 1.005^60 / (1.005^60 - 1) = about $483.32; total payments are about $28,999 and interest about $3,999.
How to interpret the result
Changing payment frequency changes both the converted periodic rate and the number of installments. The result is a comparison under a regular payment convention, not a statement that a lender must accept daily, weekly, or half-month payments.
Common mistakes to avoid
Do not use the payment frequency as the compounding frequency unless the contract actually matches. Keep a fixed installment in dollars per selected period. Do not read the payment label as monthly when the page says weekly, quarterly, or another frequency.
Assumptions and limitations
The engine uses nominal-rate conversions and does not simulate a row-by-row schedule or lender-specific day counts. It does not include fees, irregular payments, capitalization events, minimum-payment constraints, or variable rates. Invalid low installments can produce non-useful logarithms.