Guide

The Complete Guide to Free Online Calculators

From checking your BMI to working out a loan payment, calculators answer everyday questions in seconds. Quill Tools offers a set of free, accurate calculators that run entirely in your browser — nothing you enter is stored or sent anywhere. This guide covers each calculator, the formula behind it, and when to use it.

Free foreverNo sign-upRuns in your browser
01

BMI Calculator

Body Mass Index estimates whether your weight is healthy for your height using the formula BMI = weight (kg) ÷ height (m)². A result under 18.5 is underweight, 18.5–24.9 is normal, 25–29.9 is overweight, and 30+ is obese. It's a quick screening number — useful as a starting point, not a full health assessment.

02

Age Calculator

Find an exact age — or the time between any two dates — in years, months, and days. Handy for birthdays, eligibility checks, anniversaries, and forms that need a precise age as of a specific date. It accounts for leap years automatically.

03

Percentage & Unit Calculators

Calculate a percentage of a value, percentage change, or what percent one number is of another — for discounts, tips, grades, and statistics. Need to switch measurements? The unit converter handles length, weight, temperature, and more between metric and imperial.

04

Loan & EMI Calculator

Work out the monthly payment (EMI) on a loan from the principal, interest rate, and term, and see the total interest you'll pay over its life. Essential for comparing car loans, home loans, and personal loans before you commit — adjust the numbers to find a payment you can afford.

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Every tool in this guide is free, private, and runs entirely in your browser.

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