Percentage calculator
Three of the most common percentage questions, in one place: what is X% of a number, what percent one number is of another, and the percentage change between two values. Pick a mode and the calculator shows both the answer and the calculation behind it.
How to use this calculator
Choose one of the three modes, and the input labels update to match. In "% of a number" you enter a percentage and a value to find the portion. In "X is what % of Y" you enter two numbers to find what slice the first is of the second. In "% change" you enter an old and a new value to see how much it rose or fell in percentage terms.
The three formulas
Percent of a number
For example, 15% of 200 is (15 ÷ 100) × 200 = 30. This is the everyday case behind discounts, tips, and tax.
X is what percent of Y
For example, 30 out of 200 is (30 ÷ 200) × 100 = 15%. Useful for scores, completion rates, and "what share is this" questions.
Percentage change
Going from 200 to 250 is ((250 − 200) ÷ 200) × 100 = +25%. A negative result means a decrease. This is the formula behind price changes, growth rates, and "up or down how much."
A common trap: percent change isn't symmetric
A rise and the matching fall use different bases, so they don't cancel. If a $100 item goes up 50% to $150, then drops 50%, you land at $75 — not back at $100 — because the second 50% is taken from the larger $150. This catches people constantly with prices, salaries, and investment returns. When in doubt, calculate each step from its own starting value rather than adding and subtracting percentages.
Frequently asked questions
How do I add tax or a tip with this?
Use "% of a number" to find the tax or tip amount, then add it to the original. For a quick total, remember that adding 8% is the same as multiplying by 1.08. Our tip calculator does the gratuity version for you, including splitting the bill.
What does a negative percentage change mean?
It means the value went down. A result of −20% means the new figure is 20% lower than the old one. The calculator shows the sign so you can tell an increase from a decrease at a glance.
Why can't I divide by zero?
Finding "what percent of zero" or a change from zero has no defined answer, because it would require dividing by zero. If you enter zero as the base, the calculator will flag it instead of showing a misleading number.