Percentage Calculator
Four calculators in one: find a percentage of a number, find what percent one number is of another, calculate a percent increase or decrease, or work backward to find the whole.
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About this percentage calculator
Percentage questions come in more shapes than a single formula can answer, so this tool covers the four that come up most often and lets you switch between them without leaving the page. Each mode uses the same underlying arithmetic — a percentage is just a ratio scaled to 100 — but rearranged to solve for whichever piece of information you are missing that day.
"X% of Y" answers the most common version: if a bag of rice is marked 15% protein and weighs 2 kilograms, how much protein is that in grams. "X is what % of Y" flips the question around: if you scored 42 out of 60 on a test, what percentage is that. "Percent change" compares two values over time or across a change — a salary that moved from one figure to another, a population that grew or shrank — and reports both the percentage and whether it was an increase or a decrease. "Find the whole" solves the reverse case that trips people up most often: if 18 is 24% of some number, what is that number.
A quiet but important detail lives in the percent-change mode: percentage change is not symmetric. Going from 50 to 100 is a 100% increase, but going from 100 back to 50 is only a 50% decrease, not 100%. This calculator always divides by the original (starting) value, which is the standard convention used in finance, statistics, and everyday reporting, so the numbers you get here will match what a spreadsheet or a business report would show.
This page intentionally keeps to the four general-purpose modes rather than growing tabs for every specific use case. If you are working out a discount, a tip, or an exam grade specifically, dedicated calculators built for those exact situations handle the rounding conventions and terminology each one expects more precisely than a generic percentage tool can.
All values stay in your browser tab; nothing is sent anywhere, and there is no limit on how many times you recalculate.
Frequently asked questions
How do I calculate a percentage of a number?
Use the "X% of Y" mode. Enter the percentage in the first field and the base number in the second — for example, 15% of 200 gives 30. The formula is (percentage ÷ 100) × base number.
How do I find out what percent one number is of another?
Use "X is what % of Y." Enter the part in the first field and the whole in the second — for example, 42 out of 60 gives 70%. The formula is (part ÷ whole) × 100.
Why is a 50% decrease not the reverse of a 50% increase?
Percent change is always calculated against the original starting value, not the new one. 100 increased by 50% is 150, but 150 decreased by 50% is 75, not back to 100 — the base changed. This is standard convention across finance and statistics.
How does "find the whole" work?
It answers "X is Y% of what number?" Enter the known part and the known percentage, and it solves for the original whole using the formula part ÷ (percentage ÷ 100). For example, if 18 is 24% of a number, that number is 75.
Does this handle negative percentages or values?
Yes, all four modes accept negative numbers, which is useful for percent-change calculations where a value has decreased below its starting point or gone negative (for example, a swing from profit to loss).