How We Verify Our Calculators
True Calculator publishes 312 calculators. A site that size could easily be a pile of auto-generated pages that nobody checks. This page is the answer to that concern: it describes exactly how each formula gets verified, and every calculator page carries its own verification record so you can see the specific cases that were tested rather than taking the claim on trust.
What appears on every calculator page
Below the calculator itself, each page states three things: who checked the maths, the date they checked it, and the specific cases they verified. For example the BMI calculator records that the formula was confirmed against 70 kg at 1.75 m (22.86), that both the WHO and Asia-Pacific band thresholds are applied, and that mixing centimetres with kilograms raises an error rather than silently returning a wrong number.
That specificity is the point. A page claiming it was “verified” without naming a case proves nothing. Where a page has not yet had an individual review pass, it says so plainly and attributes the check to the automated test suite instead.
Three layers of checking
- Unit tests against known values. Every formula has assertions in an automated suite of roughly 1,900 tests. Each one pins the function to a value we can check by hand or against a published example, rather than to whatever the previous version happened to return.
- Edge cases as a rule, not an afterthought. Zero, negative, boundary and mismatched-unit inputs are covered explicitly. A calculator that returns a plausible-looking number for an impossible input is worse than one that refuses, so unit mismatches and out-of-range values raise an error.
- Manual review of the maths and the copy. 27 of 312 calculators have had a formula-by-formula review by a named person. The remainder carry an explicit automated-check attribution while they wait their turn.
Where the formulas come from
We do not invent formulas. Where a named standard, statute or published equation exists, we use it and cite it. The main references:
| Calculator area | Reference used |
|---|---|
| BMI and body composition | WHO Body Mass Index classification tables and the Asia-Pacific cut-off agreed at the WHO Regional Meeting for Asia, Pacific Region, 2000. |
| Basal metabolic rate | Mifflin-St Jeor equation, published in the American Journal of Clinical Nutrition, 1990. |
| Glomerular filtration rate | CKD-EPI creatinine equation, KDIGO 2012 and the 2021 CKD guideline update. |
| Pregnancy and gestation dating | Naegele's rule, with the first-trimester ultrasound dating standard used when the LMP is uncertain. |
| Home loan and reducing-balance interest | Standard annuity amortisation schedule; RBI housing loan norms for tenure and prepayment treatment. |
| Gratuity | Payment of Gratuity Act, 1972, Section 4 — the 15-day-of-last-drawn-wage formula for completed years and the 7-day ceiling for incomplete years. |
| Income tax | CBDT notification for the applicable assessment year, new regime slab tables, with the Section 87A rebate ceiling applied before slab evaluation. |
| Provident fund and pension | Employees' Provident Funds Scheme, 1952 and EPFO rate notifications; the EPFO minimum wage ceiling for the contribution base. |
| Stamp duty and registration | The Indian Stamp Act, 1899 as amended by each state, plus the respective state registration act. Rates change, so the as-of date is shown on each page. |
| Construction quantities | Indian Standard modular brick dimensions (190 × 90 × 90 mm with 10 mm mortar joint) and CPWD/NPWD scheduled-item conventions for cement and aggregate bulking factors. |
| Currency and inflation | Reserve Bank of India reference rate series and CPI base-year revisions published by the National Statistical Office. |
Data that changes over time
Tax slabs, interest rates, stamp duty and benefit limits change with government notification, sometimes mid-year. Pages built on that data carry the as-of date of the rate they are using, and the figure is labelled in the result rather than buried in a footnote. If you are making a real financial or legal decision, confirm the current rate against the source linked on the page.
What we will not do
- Publish a calculator page without a verification record.
- Present medical, tax or legal output as professional advice. These tools screen and estimate; they do not diagnose, file, or advise.
- Keep a page live that we cannot defend as genuinely useful. If a calculator duplicates another one or has no real use, it should be merged or removed rather than kept for coverage.
Found a mistake?
Please tell us. Include the calculator, the inputs you used and what you expected instead. Corrections get fixed and the review date on the page updates. Contact us or read more about the project.