Percentage Calculator

Percentage questions come in four distinct shapes, and most confusion is really about picking the right one, not the arithmetic. This calculator keeps them as four separate rows so you match your question to the right mini-calculator instead of guessing which way to divide.

X% of Y — finding a share of a number

This is the everyday case: a tip, a tax, a discount, a commission. Multiply Y by X and divide by 100. 15% of 240 is (15 ÷ 100) × 240 = 36. It answers 'how much is this slice worth' when you already know the percentage.

X is what % of Y — finding the share itself

Use this when you have two numbers and want the relationship between them expressed as a percentage — a test score out of a total, units sold against a target, or a portion of a budget. Divide X by Y and multiply by 100: 18 is what % of 60 → (18 ÷ 60) × 100 = 30%.

X is Y% of what — finding the whole

This runs the first case backwards: you know the part and the percentage, and need the original total. If $36 is 15% of a bill, the bill is 36 ÷ (15 ÷ 100) = $240. Useful for reconstructing a full price from a discounted amount, or a total from a known share.

Percentage increase or decrease

This compares an old value to a new one and reports the change as a signed percentage: (new − old) ÷ old × 100. Going from 80 to 100 is +25%. Going from 100 back to 80 is −20%, not −25% — the percentage change is never symmetric because the base is different each direction, which is the single most common mistake in this kind of calculation.