Methodology · AU-HOME-012
How the Refinance Break-Even Calculator works
This page documents how the Refinance Break-Even Calculator produces its figures: the engines and formulas it runs, the rule packs it reads statutory values from, the official documents those packs cite, and how the engines are verified.
Engines and formulas
- E07 · Scheduled mortgage ledger
A payment-period ledger with dated events (rates, extras, offsets, fees), §13.9 offset treatment and §12.5.8 reconciliation invariants on every period. Daily accrual is not modelled at P0.
Registered formulas: §13.7 recurrence · §13.9 offset
- E11 · Amortising loan engine
Closed-form §13.5 payment (with §13.6 balloon), then a full §13.7 schedule with per-period cent rounding and a capped final-payment adjustment.
Registered formulas: §13.5 payment · §13.6 balloon · §13.7 recurrence
Verification
Engines carry boundary tests at every bracket edge, property-based tests, reconciliation invariants and, where official worked examples exist, tests that reproduce them exactly. The full source register is on the sources page.