How we check our tools

People make real decisions with calculators, so accuracy matters more than anything else on this site. This page explains how we build and maintain every tool.

1. Standard formulas only

We use formulas published by recognised authorities or in peer-reviewed research, for example the standard amortization formula for loans, the WHO and NICE BMI categories, the Mifflin-St Jeor equation for calorie needs and Naegele's rule for due dates. The formula is written out on each page.

2. Cited primary sources

Each tool lists the sources it relies on: government sites such as GOV.UK, CBIC and travel.state.gov, standards bodies such as NIST and ISO, and clinical bodies such as the WHO, NHS and ACOG.

Medical review

Every health and medical calculator is reviewed by Dr Husain Farooq, medical doctor and biochemistry educator, who checks the formulas, units, reference ranges and safety advice against current clinical guidelines. The review date is shown on each page.

3. Tested against worked examples

Before a tool goes live its results are checked against worked examples from the cited source and against independent calculators.

4. Scheduled reviews

Every page is reviewed on a regular schedule. Tax rates, passport photo rules and other official requirements are rechecked whenever governments announce changes, and the review date is shown on each page.

5. Corrections

If you find an error, email hello@everydaytoolnest.com. We fix confirmed errors promptly and update the review date.

Limits

Our tools give estimates for general information. They are not legal, tax, financial or medical advice.