How to Calculate a Percentage (Simple Formulas + Free Tool)

Percentages come up everywhere — discounts, tips, taxes, grades, and statistics. Once you know the three core formulas, every percentage question is easy. Or just use the free Percentage Calculator.

1. What is X% of Y?

Multiply: Y × (X ÷ 100).

Example: 15% of 200 = 200 × 0.15 = 30.

2. X is what percent of Y?

Divide and multiply by 100: (X ÷ Y) × 100.

Example: 30 is what percent of 200? (30 ÷ 200) × 100 = 15%.

3. Percentage increase or decrease

Use the change over the original: ((new − old) ÷ old) × 100.

Example: from 200 to 230 → (30 ÷ 200) × 100 = 15% increase. A negative result is a decrease.

Try it instantly

The Percentage Calculator does all three for you. For shopping math, the Discount Calculator and VAT Calculator are purpose-built.

Frequently asked questions

How do I add a percentage to a number? Multiply by (1 + percent ÷ 100). Adding 15% to 200 → 200 × 1.15 = 230.

Is my data uploaded? No. Everything calculates in your browser.

Troubleshooting common mistakes

• A percent increase then the same percent decrease doesn't return to the start. Going up 20% from 100 gives 120; dropping 20% from 120 gives 96, not 100 — each percentage is taken of a different base. This trips people up on discounts and markups constantly.
• You divided by the wrong number in "percent change." Always divide by the original (old) value, not the new one. (230 − 200) ÷ 200 is 15%, but ÷ 230 gives a misleadingly smaller 13%.
• Percentage points vs. percent. A rate moving from 5% to 7% is a rise of 2 points, but a 40% increase. State which you mean to avoid confusion.