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.

Checks you can reproduce

These examples exercise the basic arithmetic. They do not certify every possible input or reproduce every lender's contract. No independent professional certification is claimed.

1. Budget calculator: income of 18,000 minus fixed spending of 9,000, variable spending of 4,500, savings of 1,500 and debt payments of 1,200 leaves 1,800. Dividing that unallocated surplus by the assumed 30-day month gives 60 per day.
2. Zero-interest loan: 12,000 borrowed over one year with 12 monthly payments gives 1,000 per payment, 12,000 repaid and zero interest, excluding fees.
3. Savings goal: a target of 12,000 with 2,000 already saved leaves 10,000 to fund. At zero interest the monthly estimate divides that by days remaining ÷ 30.44, rather than a calendar-month count; the page also shows weekly and daily equivalents.
4. Compare the displayed result with the worked example on each calculator page and report discrepancies.

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.