Methodology & sources
Our credibility rests on one thing: using the right standard for the right country, and showing our work. Here is exactly where our numbers come from and how we keep them current.
Reviewed by the WorldCalculators editorial team · Last updated June 2026
WorldCalculators.org implements each calculation from the primary national authority for the country you select (WHO, IRS, HMRC, JASSO, OECD and others), runs everything client-side with no tracking, reviews tax and health data at least once per tax year, and publishes a visible correction policy.
Where our data comes from
We only use primary sources — the official body that actually defines a standard in each country — never a second-hand calculator. Below are the main authorities we cite, grouped by domain.
Health
- World Health Organization (WHO) — international BMI categories
- WHO Western Pacific / IASO — Asia-Pacific BMI thresholds
- Japan Society for the Study of Obesity (JASSO) — Japanese BMI standard
- Working Group on Obesity in China (WGOC) — Chinese BMI cut-offs
- UK NHS — BMI guidance and Schofield BMR equation
Finance & Tax
- US Internal Revenue Service (IRS) — federal income tax brackets
- US Social Security Administration — FICA / Social Security & Medicare rates
- UK HM Revenue & Customs (HMRC) — Income Tax & National Insurance
- India Income Tax Department — old and new regime slabs
- OECD Tax Database — cross-country comparison
- National central banks & statistics offices — CPI / inflation series
Education
- National grading authorities and university scales (US 4.0, UK Honours, German 1–4, Australian HD)
- Published GPA conversion tables from accredited institutions
Conversion & Units
- BIPM / SI — International System of Units
- NIST — unit definitions and conversion factors
How we build each calculator
- 1. Identify the governing standard. For every calculation we determine which body sets the rule in each supported country, and where countries genuinely differ.
- 2. Implement the official formula. Formulas, brackets and thresholds are transcribed directly from the authority's published figures and unit tested against worked examples.
- 3. Surface the country differences. Each page leads with a direct answer and a side-by-side comparison so the contrast between countries is explicit, not hidden.
- 4. Cite the sources. Pages list the authorities relied on and the date the data was last reviewed.
Review & update cadence
Tax brackets, contribution rates and inflation series are reviewed at the start of each tax year and whenever an authority announces a change. Health and unit standards change rarely and are reviewed when the governing body issues new guidance. The review date shown on each calculator reflects its most recent check.
Corrections policy
If you spot a figure that looks wrong, please tell us. We verify reported issues against the primary source and correct confirmed errors promptly, updating the page's review date when we do.
Frequently asked questions
How accurate are the calculators?
Every formula is implemented from the primary national authority for that country (for example, HMRC for UK tax or JASSO for Japanese BMI). Results are estimates for educational use and may differ from an official assessment that accounts for your full personal circumstances.
How often is the data updated?
Tax brackets, contribution rates and CPI figures are reviewed at least once per tax year and whenever an authority publishes a change. Each calculator page shows when its sources were last reviewed.
Why do your results sometimes differ from other calculators?
Most calculators silently assume one country. We apply the standard for the country you select — so a BMI of 24 reads as "normal" under WHO but "overweight" under the Japanese (JASSO) standard. The difference is the point.
Do you store or sell my data?
No. All calculations run in your browser. We have no ads, no trackers and no accounts, so your inputs never leave your device.
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