Percentage Calculator

Percentage Calculator with three modes

"Percent" simply means "per hundred," and almost every percentage question on Earth boils down to one of three shapes. This calculator covers all three so you don't have to remember which formula goes with which question — just pick the mode that matches what you're trying to find.

What is X percent of Y?

This is the classic "find the slice" question — what is 20% of 80? Convert the percent to a decimal by dividing by 100, then multiply by the number: (20 ÷ 100) × 80 = 16. It's the formula behind tips, taxes, discounts, and commissions.

X is what percent of Y?

Flip the question around: 16 is what percent of 80? Divide the part by the whole and multiply by 100: (16 ÷ 80) × 100 = 20%. This is how you turn a raw score, a count, or a fraction into a percentage you can compare at a glance.

Percentage increase and decrease (change)

When a value moves from one number to another — a price, a population, a metric — the percentage change tells you how big that move was relative to where it started: ((new − old) ÷ |old|) × 100. A positive answer is an increase, a negative answer is a decrease, and zero means no change at all.

How to calculate percentages by hand

You don't need a calculator to handle most percentage problems — a little mental math goes a long way. To find a percent of a number, move the decimal point two places to the left to convert the percent to a decimal (20% → 0.20), then multiply. To find what percent one number is of another, divide the smaller (the part) by the larger (the whole), then move the decimal two places to the right to read it as a percentage. To find a percentage change, work out the difference between the two values, divide by the starting value, and again shift the decimal two places to the right.

The three formulas this tool uses are:

% of: result = (percent ÷ 100) × base
is what %: result = (part ÷ whole) × 100
% change: result = ((to − from) ÷ |from|) × 100

Percentage change vs percentage points

These two phrases sound interchangeable but mean very different things, and mixing them up is one of the most common percentage mistakes. A percentage point is the plain arithmetic difference between two percentages — going from 10% to 15% is a rise of 5 percentage points. A percentage change, on the other hand, measures that same move relative to where it started: ((15 − 10) ÷ 10) × 100 = 50%, so it's also a 50% increase. Both statements are true about the same move; they're just answering different questions, and choosing the wrong one can make a change look much bigger or smaller than it really is.

Everyday examples

Discounts and sale prices

A 25%-off sale on an $80 item: use "% of" mode to find the discount (25% of 80 = 20), then subtract it from the original price to get the $60 sale price. The same approach works for markups and price increases — just add instead of subtract.

Tips and service charges

Tipping 18% on a $45 bill is "% of" mode again: 18% of 45 ≈ $8.10. Round up or down to taste, and add it to the bill total to see what you'll actually pay.

Grades and test scores

Scored 16 out of 20 on a quiz? That's "is what percent" mode: (16 ÷ 20) × 100 = 80%. Turning raw scores into percentages makes it easy to compare results across tests that don't share the same total points.

Growth, drops, and trends

Watching a metric move over time — website visits from 10,000 to 12,500, a stock price, a city's population — is exactly what "% change" mode is for. It tells you not just that something moved, but how big that move was relative to where it started, and whether it counts as growth or decline.