Methods

How the math works

Every tool links to the method behind it. Each method page shows the formula, a worked example, the rounding rule, and what the method does not cover. The examples are the same fixtures our automated tests check on every release, so these pages cannot drift from the code.

• Level-payment amortizationUsed by all tools
• Equal-cash comparison and estimated APROffer comparison
• Refinancing break-evenRefinancing
• Debt payoff simulationConsolidation
• Precomputed interest and the Rule of 78sPrecomputed payoff
• Fee-based short-term loans and per-diem interestPayday loans
• Average rates and the quote checkAverage rates
• Deferred interestStore cards

See also the glossary of loan terms and the corrections log.