Percentage, EMI and BMI: Simple Formulas Explained

Quick answer: each everyday calculation has a short formula. Below are the ones people search for most, with an example and a free calculator to check your result.

Percentage

• X% of a number: number × X ÷ 100. Example: 15% of 200 = 200 × 15 ÷ 100 = 30.
• What percent is A of B: A ÷ B × 100. Example: 30 of 200 = 15%.
• Percentage change: (new − old) ÷ old × 100. From 80 to 100 = +25%.

Use the Percentage Calculator for all three.

Discount

Savings = price × discount ÷ 100. A 20% discount on 5,000 saves 1,000, so you pay 4,000. Two discounts do not add up: 20% then 10% is 28%, not 30%, because the second applies to the reduced price. Try the Discount Calculator.

EMI (loan instalment)

EMI = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the loan, r is the monthly rate (yearly rate ÷ 12 ÷ 100) and n is the number of months. A 1,000,000 loan at 10% for 10 years gives an EMI of about 13,215. A longer tenure lowers the EMI but raises the total interest. Check yours with the EMI Calculator.

Compound interest

A = P × (1 + r/n)^(n×t). 1,000 at 10% for 2 years compounded yearly becomes 1,210. The more often interest is added, the faster it grows. The Compound Interest Calculator lets you pick yearly, monthly or daily compounding.

BMI

BMI = weight in kg ÷ (height in m)². A person of 70 kg and 1.75 m has a BMI of about 22.9. The WHO bands are underweight under 18.5, normal 18.5-24.9, overweight 25-29.9 and obese 30 or more. BMI is only a screening guide, so talk to a doctor about your health. Use the BMI Calculator.

Age and dates

Age is counted in full years, then months and days, using the real calendar. The Age Calculator also tells you your next birthday, and the Days Between Dates Calculator counts the gap between any two dates.

Word count

Writing an essay or caption with a limit? The Word Counter counts words, characters, sentences and reading time as you type.

Creators

If you make videos, try the YouTube Money Calculator and the Engagement Rate Calculator. Our guide on what a good engagement rate is explains how to read the result.