Percentage Calculator
A three-in-one percentage calculator covering the questions people actually search for: what is X% of Y (e.g. a tip or discount amount), what percent one number is of another (e.g. a test score or a completion rate), and the percentage change — increase or decrease — between two values (e.g. a price change or year-over-year growth). Switch between the three modes with the tabs above; each computes instantly as you type, using plain arithmetic with no rounding tricks or approximations.
By The Paper Room Editorial Team — Financial & Utility Tools
Frequently asked questions
How do I calculate X% of Y?▼
Multiply Y by X, then divide by 100 — for example, 20% of 150 is (20 ÷ 100) × 150 = 30. Use the first tab ('X% of Y') and this is computed for you automatically.
How do I find what percentage one number is of another?▼
Divide the part by the whole and multiply by 100 — for example, 30 is (30 ÷ 150) × 100 = 20% of 150. Use the 'X is what % of Y' tab, where X is the part and Y is the whole.
How is percentage change calculated?▼
Percentage change = ((new value − old value) ÷ old value) × 100. A positive result is an increase, a negative result is a decrease. For example, going from 80 to 100 is a +25% change: ((100 − 80) ÷ 80) × 100 = 25%.
Why isn't a 20% increase followed by a 20% decrease back to the original number?▼
Because each percentage change is calculated against a different base. Increasing 100 by 20% gives 120; decreasing that 120 by 20% gives 96, not 100 — the second calculation is 20% of a larger number. This is a common source of confusion with percentage math, and it's why the 'percentage change' tab always states which direction (increase or decrease) the result represents.
Can percentage change be more than 100%?▼
Yes, if a value more than doubles. Going from 50 to 150 is a +200% change, since the value increased by 100 (twice the original 50), and (100 ÷ 50) × 100 = 200%.