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Free online calculators that show their working

Most of the sums people look up online are small but consequential: what a loan really costs once interest is added, how much of a salary survives tax, whether a weight is healthy for a given height, how many days are left before a due date. This site answers 82 of those questions, and on every page it also shows the formula it used and a worked example with real numbers, so the answer can be checked instead of trusted blindly.

Nothing needs an account, and the maths runs inside the browser rather than on a server — the numbers typed into a salary, loan or period calculator never leave the device they were typed on.

Money: what a loan, deposit or investment actually does

Interest is where most of the surprises live. A loan repaid on a reducing balance charges interest only on what is still owed, which is why the EMI calculator prints a year-by-year schedule rather than a single figure: in the early years most of the instalment pays interest, and that is exactly why a prepayment made early saves far more than the same amount paid later. The same arithmetic runs the other way for savings — the FD, PPF and SIP calculators show how much of the final amount is money deposited and how much is growth, which is usually a more honest picture than a single maturity number.

For pay and tax, the income tax calculator works out both the old and the new regime and says which one costs less for that income, and the salary calculator turns a CTC into the amount that actually reaches the bank account after provident fund, professional tax and tax deducted. Business sums — GST, discounts, margins — work the same way, with the tax or margin split out instead of hidden inside a total.

Health: standard formulas, plainly explained

The health tools use published equations rather than invented scores: Mifflin-St Jeor for BMR and daily calories, the WHO bands plus the lower Asian-Indian cut-offs for BMI, the US Navy method for body fat, and Naegele's rule for the pregnancy due date. Each page says what the number means and, just as importantly, what it cannot tell you — BMI, for instance, cannot separate muscle from fat, which is why a fit, heavy person often lands in the "overweight" band.

Maths, school and everyday answers

The maths tools are built for homework and quick checks: percentages with the steps shown, fractions in simplified and decimal form, standard deviation for both a sample and a whole population, and a scientific calculator that keeps a history of what was typed. Everyday questions have their own tools — exact age down to the day, CGPA converted to a percentage using the right rule for the university, electricity bills estimated from units and slab rates, plus unit, currency and time zone converters.

How to trust a number from this site

Every result here is an estimate produced by a published formula, and the page says which one. For money, the lender, employer or tax department has the final word; for health, a clinician does. Formulas are tested against hand calculations and re-checked when rates change — the method, the sources and the correction process are written out in full on how we check every calculator. If a number ever looks wrong, tell us and it gets fixed.

Part of the CodingMarble family

Need more than numbers? LovePDF merges, compresses and converts PDF files, LoveImage resizes and compresses photos, the QR code generator makes UPI, WiFi and logo QR codes, and the resume and biodata maker builds a CV or marriage biodata, the typing test checks your WPM in English and Hindi, and kids learning games teach letters and numbers to young children. Worked out your calories or BMI here? Turn it into action with a free workout plan or yoga at home. Studying for an exam? CodingMarble Learn teaches Class 8–12 maths and science in 3D – all free, with no sign-up.