Percentage Calculator
Calculate percentage of a number, percentage change between two numbers, and what percent X is of Y. Fast, clean, and works with any values.
What this calculates
Percentages show up everywhere: discounts, tips, grades, growth, interest. This calculator covers the three questions people actually ask: what is X % of a number, what percent of one number is another, and what is the percentage change between two values. Pick the mode and the math is instant.
Formula & how it works
Percent of a number: result = value × (percent ÷ 100). What percent of Y is X: result = (X ÷ Y) × 100. Percentage change from A to B: change = ((B − A) ÷ A) × 100 (positive = increase, negative = decrease). All three use the basic identity that percent means 'per hundred' — 25 % is just shorthand for 0.25.
Worked example
What is 18 % of 250? → 250 × 0.18 = 45. What percent of 200 is 30? → (30 ÷ 200) × 100 = 15 %. Percentage change from 80 to 100? → ((100 − 80) ÷ 80) × 100 = 25 % increase. Going back the other way, 100 to 80 is a 20 % decrease — note that percentage change is not symmetric.
Frequently asked questions
Why isn't percent change symmetric?
Because the denominator is always the starting value. Going up from 80 to 100 is a 25 % increase (20/80). Going down from 100 to 80 is a 20 % decrease (20/100). Same absolute change, different percent — this trips people up constantly.
What's the difference between percent and percentage points?
Percentage points are the absolute difference. If interest rates go from 4 % to 5 %, that's a 1 percentage point increase but a 25 % relative increase. News headlines often confuse the two.
How do I reverse a discount?
If something is $80 after a 20 % discount, the original was 80 ÷ (1 − 0.20) = 80 ÷ 0.80 = $100. Don't just add 20 % back — that gives the wrong answer because the discount was applied to the higher number.
Can percentages exceed 100?
Yes. A value can grow by more than its original size (200 % growth means it tripled). A grade can be over 100 if there's extra credit. Only when expressing a fraction of a whole (e.g., 'what percent of the class') is the cap genuinely 100.