Skip to content
Tools Free calculators that show their working

Editorial Policy and Methodology

How we choose, build, check and update every calculator and guide on Tools.

Our standards

  • Accuracy first. A tool is only published when its results match the source method on worked examples.
  • Transparency. Every tool page names its formula, states its assumptions and lists its sources.
  • Independence. Advertising pays for the site, but advertisers have no say over our tools or content, and results are never altered for commercial reasons.
  • Plain English. We explain results in everyday language and say when a professional should be involved.

Where our figures come from

We use primary sources wherever possible, in this order of preference:

  1. Government and regulator publications, such as HMRC and GOV.UK, the IRS, the Social Security Administration, the FCA and the CFPB.
  2. Public health bodies and professional organisations, such as the NHS, NICE, the CDC, NIH and ACOG.
  3. Peer-reviewed research, cited with the authors, journal and year.
  4. Recognised standards bodies, such as NIST and ISO.

We do not use other calculator websites as sources.

How each tool is built and checked

  1. Method. We identify the standard method a professional would use and document it on the page.
  2. Implementation. The calculation is written in code that runs in your browser.
  3. Testing. Results are checked against worked examples from the source, against hand calculations and against edge cases such as leap years, zero values and very large inputs.
  4. Content. Every number quoted in an article or example on a tool page is generated by the tool itself, so the text and the calculator always agree.
  5. Review. A human editor reviews each page before publication.

Keeping tools up to date

Tools that depend on figures that change, such as tax bands, thresholds and contribution limits, show the period they apply to under “Sources and methodology”. We review them when new figures are announced, and at least once a year: UK tax tools before 6 April and US tax tools before 1 January.

Use of AI and software

We use software, including AI writing and coding assistants, to help draft explanations, write code and check for errors. AI never decides a result: every figure is produced by the calculator’s tested code, every source is a real, linked document, and a person reviews and is responsible for everything we publish.

Corrections

If you find an error, email maservices131@gmail.com. We investigate every report. Confirmed errors are corrected promptly and, where a result was materially affected, we add a dated note to the page explaining what changed.

Health content

Health tools use equations validated for healthy adults and say clearly who they are not suitable for. They are information tools, not medical devices, and they never replace advice from a doctor, midwife or registered dietitian.