Percentage Calculator

Every everyday percentage question in one place: percent of a number, percent change, what percent one number is of another, and adding or subtracting a percentage.

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Percentages Made Easy: Formulas and Examples

By the EMI Cal Hub team · Last updated October 2026

Percentages appear everywhere: discounts, exam marks, salary raises, interest rates, tips and price changes. "Per cent" simply means "per hundred", so 15% means 15 out of every 100. Once you know the handful of formulas below, almost any percentage question becomes simple.

1. What is A% of B?

Result = A × B ÷ 100. Example: 15% of 200 = 15 × 200 ÷ 100 = 30.

2. A is what percent of B?

Percentage = A ÷ B × 100. Example: 30 is what percent of 200? 30 ÷ 200 × 100 = 15%. This is how exam scores are usually turned into percentages.

3. Percentage change from A to B

Change = (B − A) ÷ A × 100. A positive result is an increase; a negative one is a decrease. Example: a price rising from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% increase.

4. Increase or decrease a number by a percentage

Increase: B × (1 + A ÷ 100) and Decrease: B × (1 − A ÷ 100). Example: 200 increased by 15% is 230; decreased by 15% is 170.

A common trap

A 20% decrease followed by a 20% increase does not bring you back to where you started. 100 down 20% is 80, and 80 up 20% is 96. That's because the second percentage is applied to a smaller number. Keep this in mind when reading about prices or investments that fall and then recover.

Percent vs percentage points

If an interest rate goes from 5% to 6%, it has risen by one percentage point, but by 20% in relative terms. News and financial reports often mix these up, so it's worth checking which one is meant.

Disclaimer: Results are estimates for planning and education only. They are not financial, tax or legal advice. Please confirm figures with your bank, tax adviser or another qualified professional before making decisions.

Frequently Asked Questions

How do I calculate a percentage of a number?

Multiply the number by the percentage and divide by 100. For example, 20% of 150 = 20 × 150 ÷ 100 = 30.

How do I calculate percentage increase?

Subtract the old value from the new value, divide by the old value and multiply by 100.

How do I find what percent one number is of another?

Divide the first number by the second and multiply by 100.

What is the difference between percent and percentage points?

Percentage points measure the simple difference between two percentages. Percent change measures the relative change. 5% to 6% is +1 percentage point, or a 20% increase.