How the repayment calculations work
Understand the assumptions, formulas, limitations and testing used by Pay Off Sooner mortgage, loan, car-finance and credit-card calculators.
Monthly amortisation model
Mortgage and conventional fixed-sum loan estimates use a monthly amortisation model. Interest is estimated from the entered annual rate divided by twelve, then the payment and any extra capital are applied. Real providers may calculate interest daily, use different allocation rules or recalculate the payment after an overpayment.
Settlement comparisons
The loan and HP/PCP settlement modes start with an official dated quote. They compare that quote with scheduled cash remaining. They do not reconstruct statutory rebate formulas or claim that the entire difference is interest.
Credit-card model
The credit-card tool compares a simplified percentage-based minimum with a fixed monthly payment. Providers can add interest, fees and a cash floor differently. Promotional rates, new purchases, balance transfers and missed payments are not included.
Safety limits
Calculations stop after 600 months and reject payment paths that do not cover modelled interest. Negative inputs are treated as zero. Results are rounded for display while calculations retain decimal values.
Testing and reporting errors
The release includes automated source, route, metadata, sitemap, schema, contrast and calculator checks. A passed test does not make an estimate an official lender figure. Report a suspected defect through the contact page with the route and figures entered.