About True Calculator

True Calculator is a collection of free online calculators built for everyday use in India. We started with the tools people actually search for most — percentage, age, BMI, home loan EMI, income tax and stamp duty — and now cover eleven categories spanning finance, health, mathematics, statistics, construction and daily life.

How we build our calculators

Every tool starts with a published formula, not an invented one. Financial calculators follow RBI norms and standard banking practice: EMIs use the reducing-balance formula Indian banks actually apply, gratuity follows the Payment of Gratuity Act's 15/26 rule with the ₹20 lakh ceiling, income tax tracks current-regime slabs, and stamp duty reflects state-specific rates including concessions where they exist. Health tools use validated clinical equations — Mifflin-St Jeor and Katch-McArdle for metabolism, CKD-EPI for kidney function, Naegele's rule for due dates, WHO and Asia-Pacific BMI cutoffs shown side by side — and each states which formula it applies. Construction quantities follow trade practice, from 1:2:4 concrete mixes to paint coverage by surface porosity.

Where authoritative sources differ, we show both rather than picking silently: BMI carries WHO and Asia-Pacific ranges together, loans can be compared across tenures side by side, and inflation tools let you choose between official CPI series of different countries.

Verification and updates

Each calculator ships with its formula, a worked example you can check by hand, and notes on common mistakes — because a result you cannot verify is just a claim. Our maths libraries are covered by an automated test suite of nearly two thousand cases, including edge conditions such as zero rates, negative inputs and boundary values, and every calculator was manually audited against published worked examples from reference sources before release. Rates that change — tax slabs, stamp duty, fuel prices — are reviewed and updated regularly, and pages carry their last-updated date so you know how fresh the assumptions are.

Privacy first, always

Every calculation runs entirely in your browser. Your numbers never leave your device — there is no sign-up, no account, no email collection and no paywall. We keep pages fast and clutter-free: no pop-ups, no autoplaying video, no interstitials between you and the answer.

What's next

We keep adding calculators based on what users ask for. If a rate looks stale, a result looks wrong or a tool you need is missing, tell us — reports with the numbers you entered get fixed fastest.