How we test our tools

Last updated: 2026-09-04

Published formulas

Each calculator page states the formula it uses. Loan and debt calculations use standard amortisation; budgeting tools use straightforward arithmetic. If you cannot check a result yourself, we have not documented it well enough.

Verification checks

1. Results are compared against manual calculations for several representative scenarios.
2. Edge cases are tested: zero values, very large values, and payments below monthly interest.
3. Invalid input is rejected with a clear message rather than producing a misleading number.
4. Rounding is applied only at display time so intermediate steps stay accurate.

Assumptions we make

• Interest compounds at a regular interval unless stated otherwise.
• Payments are made on schedule and in full.
• Rates entered are annual nominal rates.
• Fees, insurance and taxes are excluded unless you enter them yourself.

What our tools deliberately exclude

We do not model rate changes, penalty fees, promotional periods, tax treatment or provider-specific day-count conventions. Including them would create false precision, since those terms vary by contract. Compare our estimate with your provider's quote before deciding.

Reporting a problem

If a result looks wrong, send us the inputs you used through the contact page. We investigate calculation reports first.