About The Calc Library
1678 free calculators across 6 categories, built to give you an answer without an account, a paywall, or a page of filler before the tool.
Why this exists
Most calculator sites are built to serve advertising rather than answers. You land on one looking for a monthly payment and find pop-ups, a newsletter modal, and the result buried below a thousand words of padding.
This site takes the opposite approach. The tool is at the top of every page. The explanation sits below it for anyone who wants it, not in front of it as a toll. Advertising funds the site, but it is kept out of the calculator and away from its controls, see our editorial policy for exactly where the line sits.
How the calculators are built
Every tool implements a named, published formula rather than an approximation invented here: Mifflin-St Jeor for calorie needs, the 2021 race-free CKD-EPI equation for eGFR, the US Navy circumference method for body fat, the standard amortising formula for loans, Riegel's formula for race prediction. The page names the formula so you can check it yourself.
44 calculators link to primary sources: the WHO, CDC, NICE, NHLBI, NIDDK, the NHS, ACOG, the American Heart Association, the CFPB, the SEC, and peer-reviewed papers on PubMed. Every one of those links was fetched before publication to confirm it resolves and points where it claims, several candidates were dropped for 404ing or redirecting somewhere unrelated.
Calculations run entirely in your browser. Nothing you type is sent to a server, logged, or shared with anyone, which is a privacy decision and also the reason the tools work instantly.
Who builds it
Mohit Patel
Founder and maintainer. Built The Calc Library and maintains every calculator on it. Each tool implements a named, published formula rather than an approximation invented for the site, and every source link is fetched and confirmed before it goes live, candidates that returned a 404 or redirected somewhere unrelated were dropped rather than published. Error reports go to a person, not a queue, and confirmed mistakes are fixed and the page's date updated.
What is here
- Finance — Work out loan payments, investment growth, and what things actually cost.
- Health & Fitness — Track body composition, calorie needs, and the numbers behind your goals.
- Selling Online — Work out what marketplace fees leave you, and what to charge to actually make a margin.
- Printables & Generators — Make the thing rather than measure it: printable paper, puzzles, cards and templates you can send straight to a printer.
- Math & Everyday — Percentages, dates, grades, and the quick arithmetic that comes up daily.
- Science & Engineering — Mechanics, energy, circuits and solutions — with the idealisation each formula rests on stated rather than hidden.
Accuracy and limits
These tools are for planning and general information. Health calculators produce population estimates and are not medical advice. Finance and selling calculators model arithmetic, not your tax position or the specific terms you are being offered. Each page carries the relevant caution, and the terms of use set out the full position.
If a result looks wrong, tell us — corrections are the fastest way the site improves, and confirmed errors are fixed and the page's “last checked” date updated.
How the site is funded
Display advertising, and nothing else. There are no sponsored calculators, no paid placements, no affiliate links inside the tools, and no advertiser sees content before it is published. Our privacy policy covers what advertising and analytics cookies do and how to refuse them.
Contact
Error reports, calculator requests and everything else go to hello@thecalclibrary.com, or via the contact page. Every message is read by a person.