Percentage Calculator

What is X% of Y → (X ÷ 100) × Y. X is what % of Y → (X ÷ Y) × 100. X is Y% of what → X ÷ (Y ÷ 100).

Three questions, one tool

Almost every everyday percentage problem is one of three questions, and they are easy to mix up. The first is “what is X% of Y” — a tip, a discount, a tax: you have the percentage and the whole, and you want the part. The second is “X is what percent of Y” — a test score, a market share, a price change: you have the part and the whole, and you want the percentage. The third is the reverse — “X is Y% of what number” — used to find an original price before a discount, or a total from a known portion. Pick the matching mode and enter the two values you know; the calculator does the rest and shows the working.

It also gives the two equivalents people often need: the percentage as a decimal (25% = 0.25) and as a simplified fraction (25% = 1/4), which makes mental maths and spreadsheet formulas easier.

Worked examples: What is 25% of 200? → 0.25 × 200 = 50. 30 is what percent of 120? → 30 ÷ 120 × 100 = 25%. 45 is 30% of what number? → 45 ÷ 0.30 = 150.

Why sequential percentages don’t add up

The most common percentage mistake is adding changes that should be multiplied. A price raised 20% and then cut 20% does not return to where it started — it ends up 4% lower, because the second change applies to the already-changed amount. Likewise a 20% discount followed by a 10% discount is a 28% total reduction, not 30%. Whenever percentages are applied one after another, they chain (multiply) rather than add.

Enter a start value and a series of changes under the advanced options and the calculator works the chain through step by step, then shows the single equivalent percentage change. It is the honest way to handle stacked discounts, compounding markups, or a boom followed by a bust.

Percentage vs percentage point

One more distinction trips people up constantly: a percentage versus a percentage point. If an interest rate rises from 4% to 6%, that is a 2 percentage-point increase but a 50% increase (2 ÷ 4). Both are correct, and they describe very different magnitudes — which is why headlines that blur them can mislead. When you mean the relative change, use the “X is what percent of Y” mode on the difference; when you mean the absolute gap, it is simply the subtraction.

Keeping the two straight, and remembering that sequential percentages multiply, covers the vast majority of percentage errors. The rest is just the three core formulas this calculator wraps up.