Percentage Calculator

Three percentage questions, one tool

Most everyday percentage problems are one of three questions, and this calculator handles all of them. Pick the mode from the dropdown and the input labels change to match. Everything calculates instantly in your browser.

1. What is X% of Y?

This finds a portion of a number. Multiply the number by the percentage written as a decimal: X% of Y = (X ÷ 100) × Y. For example, 15% of 200 is 0.15 × 200 = 30. Use it for tips, commissions, sale amounts, or “how much is 30% of this?”

2. X is what percent of Y?

This turns a part-and-whole into a percentage: (X ÷ Y) × 100. For example, 30 out of 200 is (30 ÷ 200) × 100 = 15%. Use it for test scores, “what percentage did I complete?”, or working out a rate from raw numbers.

3. Percent change from X to Y

This measures how much a value grew or shrank: ((Y − X) ÷ |X|) × 100. Going from 200 to 250 is a +25% change; going from 200 to 150 is −25%. A positive result is an increase, a negative result is a decrease. Use it for price changes, growth rates, or before-and-after comparisons.

A quick mental-math trick

Percentages are reversible: X% of Y always equals Y% of X. So if 18% of 50 feels awkward, flip it — 50% of 18 is just 9. This is a fast way to sanity-check the calculator’s answer in your head.

FAQ

Why does percent change use the absolute value of X?

Dividing by the absolute value keeps the sign of the change meaningful even when the starting value is negative, so an increase always reads as positive and a decrease as negative.

Can the starting value be zero?

For “X is what percent of Y” and percent change, the denominator can’t be zero — there’s no meaningful percentage of nothing — so the tool will ask you to enter a non-zero value.

Which mode do I use to calculate a discount?

Use “What is X% of Y” with X as the discount percent and Y as the original price to find the amount off, then subtract it. To check a sale that already happened, use percent change from the old price to the new price.

How do I work out a tip?

Use “What is X% of Y” with X as the tip percentage (such as 15 or 20) and Y as the bill total. The result is the tip amount, which you add to the bill.

Is this percentage calculator free and private?

Yes, it is free with no sign-up, and every calculation runs in your browser, so nothing you type is uploaded. It also works on phones and tablets for quick checks on the go.