How to Calculate a Percentage

What "percent" means

The word percent means "per hundred". So 25% is just another way of writing 25 out of 100, which is the fraction 25⁄100, or the decimal 0.25. That single idea is the key to every calculation below: to use a percentage in maths, divide it by 100.

1. Find a percentage of a number

This answers questions like "What is 20% of 80?" The formula is:

(percent ÷ 100) × number

Example: 20% of 80 = (20 ÷ 100) × 80 = 0.20 × 80 = 16. This is the maths behind a tip, a discount, or sales tax on a price.

2. Find what percent one number is of another

This answers "15 is what percent of 60?" The formula is:

(part ÷ whole) × 100

Example: (15 ÷ 60) × 100 = 0.25 × 100 = 25%. Use this for a test score (got 45 out of 50 → 90%) or what share of a budget something takes.

3. Find a percentage increase or decrease

This answers "A price went from $40 to $50 — what percent did it rise?" The formula is:

((new − old) ÷ old) × 100

Example: ((50 − 40) ÷ 40) × 100 = (10 ÷ 40) × 100 = 25% increase. If the result is negative, it is a decrease. This is how you describe a raise, a price drop, or growth over time.

A few handy shortcuts

• 10% of a number: just move the decimal point one place left. 10% of 250 is 25.
• 1% of a number: move it two places left. 1% of 250 is 2.5.
• Percentages can be reversed: X% of Y always equals Y% of X. So 8% of 50 is the same as 50% of 8 = 4 — much easier to do in your head.
• To add a percentage (like tax): multiply by 1 plus the rate. To add 8%, multiply by 1.08.

Let the calculator do it

These formulas are quick once you know them, but for real numbers it is faster and safer to use a percentage calculator. Enter the values for any of the three question types and get the answer instantly — useful for discounts, tips, grades and growth rates.

Try the free Percentage Calculator →
Find a percent of a number, what % of a total, and increase/decrease.

Frequently asked questions

What is the basic percentage formula?

To find a percentage of a number, use (percent ÷ 100) × number. For example, 20% of 80 is 0.20 × 80 = 16. The key is that 'percent' means 'per hundred', so you always divide the percent by 100 first.

How do I work out a percentage increase?

Use ((new value − old value) ÷ old value) × 100. If a price rises from 40 to 50, that is ((50 − 40) ÷ 40) × 100 = 25%. A negative answer means a decrease.

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

Divide the part by the whole and multiply by 100. For a score of 45 out of 50: (45 ÷ 50) × 100 = 90%.