SumPercentage Calculator
Three percentage tools in one place: find a percentage of a number, work out what percent one number is of another, and calculate percentage increase or decrease. All three update live as you type.
How It Works
A percentage is just a fraction out of 100 — "percent" literally means "per hundred." This page covers the three percentage calculations people use most. (a) X% of Y is found by multiplying: (X / 100) × Y. (b) X is what % of Y is found by dividing: (X / Y) × 100. (c) Percentage change between an old value and a new value is ((new − old) / old) × 100 — a positive result means an increase, a negative one means a decrease.
These three cover almost every everyday percentage question: sale discounts and tips use (a), test scores and completion rates use (b), and price changes, salary raises, and investment returns use (c). One common trap is percentage points versus percent: if a rate rises from 20% to 25%, that is a 5 percentage point rise but a 25% percent increase, because 5 is 25% of 20.
Worked examples: (a) 20% of $250 = (20 / 100) × 250 = $50 — so a 20% discount on a $250 item saves you $50. (b) 45 out of 180 = (45 / 180) × 100 = 25% — so scoring 45 out of 180 is a 25% score. (c) A price rising from $120 to $150 is ((150 − 120) / 120) × 100 = +25%, a 25% increase.
Frequently Asked Questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For 20% of 250: (20 / 100) × 250 = 50.
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. For example, 45 is (45 / 180) × 100 = 25% of 180.
How do I calculate percentage increase or decrease?
Subtract the old value from the new value, divide by the old value, and multiply by 100. A price going from $120 to $150 is a 25% increase; a price falling from $150 to $120 is a 20% decrease.
What is the difference between percent and percentage points?
Percentage points measure the simple difference between two percentages: 25% minus 20% is 5 percentage points. Percent change is relative: that same move is a 25% increase, because 5 is 25% of 20.
Can percentages be over 100%?
Yes. A value can be more than 100% of another — 250 is 125% of 200. And a percentage increase can exceed 100%: doubling a price is a 100% increase, tripling it is a 200% increase.
Last updated: November 2026