Percentage Calculator

How do you calculate a percentage? A percentage is just a fraction of 100, and all percentage math comes down to three formulas:

1. What is X% of Y? Multiply: (X ÷ 100) × Y. Example: 15% of 80 = 0.15 × 80 = 12.

2. X is what percent of Y? Divide and scale: (X ÷ Y) × 100. Example: 25 of 200 → 25 ÷ 200 × 100 = 12.5%.

3. Percentage change from X to Y: ((Y − X) ÷ X) × 100. Example: a price going 40 → 50 is (10 ÷ 40) × 100 = +25%.

The calculator above runs all three at once — type into whichever question matches yours and the answer appears instantly.

This percentage calculator solves the three problems people actually search for, side by side: finding a percentage of a number (tips, discounts, tax), expressing one number as a percentage of another (test scores, market share, progress), and percentage increase or decrease (price changes, growth rates, weight loss).

Worked examples: a 20% tip on a $64 bill is 0.20 × 64 = $12.80. Scoring 42 out of 50 on a test is 42 ÷ 50 × 100 = 84%. Rent rising from $1,200 to $1,320 is a (120 ÷ 1200) × 100 = 10% increase. The mental-math shortcut worth knowing: 10% is “move the decimal one place left” (10% of 250 = 25), and other percentages build from it — 5% is half of that, 20% is double, 15% is one-and-a-half times.

One trap the third calculator handles correctly: percentage change is always measured against the starting value. A fall from 50 to 40 is −20%, but climbing back from 40 to 50 is +25% — same distance, different base. Everything computes instantly in your browser.