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KazamTools

Methodology: How Our Calculators Are Built and Checked

Where every formula comes from, how we test it, and how we keep it up to date.

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KazamTools has 216 free tools, 95 of them finance, tax or health calculators where a wrong answer can cost someone money or affect a health decision. This page explains the process each of them goes through before it is published and after. Who writes and checks the content is covered in our editorial policy.

1. Start from a published source

Every calculator starts from a formula or a rule that someone accountable has published. We do not invent formulas or average numbers from other calculator sites.

  • Tax and payroll: the tax authority's own tables and worked examples, such as IRS Publication 15-T and Revenue Procedures, HMRC rates and thresholds, India's Finance Act and Income Tax Department, and Pakistan's Finance Act and FBR circulars.
  • Loans and savings: the standard amortization and compound-interest formulas, with terms such as APR and PMI defined as the US Consumer Financial Protection Bureau and Regulation Z define them.
  • Health: the equations used by public-health bodies and in peer-reviewed papers, for example the WHO and CDC BMI cut-offs and the Mifflin-St Jeor equation for resting energy.
  • Units: exact definitions from NIST Special Publication 811 and the UK Weights and Measures Act, so 1 inch is exactly 2.54 cm and 1 pound exactly 0.45359237 kg.

Each finance, tax and health page lists the sources it relies on in its "How we keep this tool accurate" box.

2. Write the maths once, separate from the page

The formulas for each tool live in their own small module, apart from the buttons and inputs you see. That keeps the maths easy to read and review, and it means the result on the page, in an embedded widget and in our tests always comes from the same code.

  • We keep full precision through every step and round only the final figure you see.
  • Money is shown to the cent (or paisa); tax tools follow the rounding rules the tax authority states.
  • Where a rule depends on a date, such as a tax year or a leap year, the date logic is written and tested on its own.

3. Test against known correct answers

Every calculator has automated tests that compare its output with answers we know are right: the worked examples printed in official guidance where they exist, hand-checked figures otherwise. The tests also cover the awkward cases: zero, negative and very large numbers, empty inputs, the edges of every tax band, and 29 February.

The whole test suite runs before every release. A change that breaks a known answer cannot be deployed. Browser tests then open every page and check that it loads, that the tool works and that nothing on the page is broken.

4. Show the working

A result you cannot check is hard to trust. Our calculators show the formula they used and, where it helps, the working with your own numbers, plus a worked example in the article under the tool. If our answer differs from another calculator, you can see exactly why.

5. Review and keep it current

  • Every finance, tax and health page shows who wrote it and the date its rules were last reviewed.
  • Tax tools are tied to a named tax year. We re-check them when new rules are announced: the US each autumn when the IRS publishes the next year's inflation adjustments, the UK at each Budget and at the start of the tax year on 6 April, India after the Union Budget on 1 February, and Pakistan after the federal budget in June.
  • When a rule changes, we update the code and its tests together, then move the page's review date.
  • Finance, tax and health pages name a qualified reviewer when one has checked them. We never list a reviewer or a credential that we cannot back up.

6. File tools: private by design

PDF, image, video and text tools process your files inside your browser. Files are not uploaded to our servers, so there is nothing for us to store, read or lose. Some AI tools download a model to your device the first time you use them; the model then runs locally.

7. Corrections

If you think a result is wrong or a rule is out of date, please tell us and include the numbers you entered. We check every report, fix confirmed errors with a test so they cannot come back, and update the page's review date.

This methodology is maintained by Awais, founder and editor-in-chief.