Guides

Short, plain-language guides to the calculations people ask about most. Each guide links to the matching calculator.

How to calculate a loan EMI

EMI = P × r × (1+r)ⁿ ÷ ((1+r)ⁿ − 1), where P is the loan amount, r the monthly rate (annual rate ÷ 12 ÷ 100) and n the number of months. A longer term lowers the EMI but raises the total interest. Try the Loan EMI or Mortgage calculator.

Understanding BMI

BMI = weight (kg) ÷ height (m)². Under 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese for most adults. BMI ignores muscle and age, so treat it as a screening guide only. Use the BMI calculator.

Simple vs compound interest

Simple interest is earned only on the original amount; compound interest is earned on the amount plus past interest, so it grows faster over time. Compare with Simple Interest and Compound Interest.

Percentage made easy

X% of Y = X ÷ 100 × Y. Percent change = (new − old) ÷ old × 100. See Percentage and Percent Change.

Ohm’s law basics

V = I × R and P = V × I. With any two values you can find the rest. Try Ohm’s Law, Voltage Divider and LED Resistor.

Binary, octal and hexadecimal

Computers use base 2; programmers also use base 8 and 16 because they map neatly onto binary. Convert any number with the Binary Octal Hex Converter or practise with the Bitwise Calculator.

Converting units

Multiply by the right factor: 1 km = 0.621371 miles, 1 kg = 2.20462 lb. Use the Length, Weight and Temperature converters.