What Percentage Calculator Does and Why It Matters
Percentage Calculator covers the handful of percentage questions people actually run into day to day: what a percentage of a number is, what percentage one number is of another, and what percentage increase or decrease happened between two values. Each is a different formula, and it's easy to reach for the wrong one under time pressure — this tool keeps them separate so you pick the calculation that matches your actual question instead of reverse-engineering a formula.
These come up constantly: working out a discount or tip, checking how much a price or metric changed, or converting a raw score into a percentage. Getting the increase/decrease direction right in particular trips people up by hand, since a 20% increase and then a 20% decrease don't cancel out to the original number.
How to Use Percentage Calculator
- Pick the calculation mode that matches your question (e.g. "X% of Y", "X is what % of Y", or "% change from X to Y").
- Enter the numbers into the fields for that mode.
- The result is calculated and shown immediately.
- Switch modes at any time to ask a different kind of percentage question.
The Formulas Used
- X% of Y: (X ÷ 100) × Y
- X is what % of Y: (X ÷ Y) × 100
- Percentage change from X to Y: ((Y − X) ÷ X) × 100 — positive for an increase, negative for a decrease
Privacy and Security
The numbers you enter are used only to calculate the result on the page and are never sent anywhere or stored.
Frequently Asked Questions
Why doesn't a 20% increase followed by a 20% decrease return the original number?
Because each percentage is calculated against a different base value. A 20% increase on 100 gives 120; a 20% decrease is then calculated on 120, not 100, giving 96 — not back to 100. This is a common source of confusion, not a calculation error.
What's the difference between "percentage of" and "percentage change"?
"X% of Y" answers a proportion question (like a tip or discount). "Percentage change" measures how much a value moved between two points and needs both a starting and ending value, not a single number and a percentage.
Can this handle negative numbers or values over 100%?
Yes — percentage change can exceed 100% (more than doubling) or be negative (a decrease), and the calculator handles both correctly.