Category · 4 tools
Free calculators that show their working
Some numbers are needed immediately and a spreadsheet is overkill: a tip percentage, an exact age for a form, a BMI reading after a check-up, the monthly cost of a loan. These calculators are small, fast and show the formula next to the result, so you can check the answer instead of trusting a black box.
All four run entirely in your browser. Inputs are never uploaded, nothing is saved between visits, and the pages state the assumptions behind each number — BMI is a screening indicator rather than a diagnosis, and a loan payment excludes taxes, fees and insurance. For anything consequential, use the calculator as a second opinion rather than the final answer.
In this category
Percentages, age, BMI and loan maths
Small calculators, formulas on the page
Every calculator here is built around one standard formula and prints that formula next to the result. That matters more than it sounds: a percentage that looks wrong is usually a question of which base was used, and a loan payment that surprises you usually excludes fees or assumes a different compounding interval. Seeing the working lets you check the answer against your own numbers instead of trusting an unknown website.
Inputs stay in the browser. Birth dates, income figures and health data are exactly the kind of information people should not have to upload to a random server, so nothing here is transmitted or stored. For decisions with real consequences — medical, financial or legal — use these results as a quick estimate and confirm with a professional who knows your situation.
- A discount or tip on the spot
- Percentage Calculator handles percent-of, what-percent and increase/decrease in one place.
- A form asking for exact age
- Age Calculator gives years, months and days plus total days and the next birthday countdown.
- Checking a monthly repayment
- Loan Calculator turns principal, rate and term into a monthly payment and total interest — before fees and insurance.