About the calculator
All calculations are performed locally in your browser. No data is sent to a server.
How it calculates
The calculator uses standard banking formulas. The annuity payment follows the formula P · r / (1 − (1+r)⁻ⁿ); the differentiated payment divides the principal by the number of months and recomputes interest on the remaining balance. Early repayment is applied in the chosen month and the schedule is rebuilt (either a shorter term or a lower payment). The reverse calculation solves the annuity equation with Newton-Raphson.
All arithmetic is performed locally in your browser using decimal.js — no input ever leaves your device.