Percentage Calculator

About this Percentage Calculator

Find a percent of a number, what percent X is of Y, or the percentage change between two values, with working shown. It is one of the Calculators and Generators on ToolUstad, and like every tool here it runs entirely in your browser: nothing you type, paste or open is uploaded to a server, and there is no sign-up or usage limit.

What is a percentage?

A percentage is a fraction out of 100: 25 percent means 25 per hundred, written 25%. Percentages let you compare parts of different sized wholes on one scale, which is why they run through discounts, tax, exam marks, interest, growth rates and statistics. Nearly every everyday percentage question is one of three shapes, and this calculator handles all three with the formula shown, so you can check the working rather than trust a bare answer.

The three calculations, with formulas

Problem	Formula	Example
What is X% of Y?	(X / 100) x Y	20% of 80 = 16
X is what % of Y?	(X / Y) x 100	30 of 120 = 25%
Percentage change	((New - Old) / Old) x 100	80 to 100 = +25%

When and why to use it

Shopping: work out the real price after a 30 percent discount, and the tax on top.
School and exams: convert marks like 47 out of 60 into a percentage.
Business: margins, growth rates, and changes in revenue or costs.
Money: interest, tips, commission and salary increases.
Health and cooking: body fat changes, recipe scaling and discounts on ingredients.

Best practices

For discounts, calculate the saving and subtract it: 30 percent off 50 is 15 saved and 35 paid.
Sanity check with round numbers: 10 percent is a tenth, 50 percent is half.
Remember percentage points are not percent: a rise from 4% to 5% is 1 percentage point, but a 25 percent increase.

Common mistakes to avoid

Adding percentages that have different bases, like two successive discounts: 20% then 10% off is 28% off, not 30%.
Dividing by the new value instead of the original in a change calculation.
Reversing a percentage wrongly: taking 20% off then adding 20% does not return the starting price.

Who is the percentage calculator for?

Students, shoppers, teachers, accountants and business owners: anyone who meets percentages outside a classroom. The three formulas are easy to misremember under pressure; the calculator applies the right one and shows the working, so the answer can be checked and reused with confidence.

Percentages in real decisions

Two money examples show why the working matters. A salary rising from 50,000 to 54,000 is an 8 percent increase, ((54,000 - 50,000) / 50,000) x 100, not the 7.4 percent you get by dividing by the new salary. And a product bought for 80 and sold for 100 carries a 25 percent markup on cost but a 20 percent margin on price, which is why business arguments about "the percentage" so often talk past each other. Naming the base, and using the change mode of this calculator which divides by the original value, ends the argument with arithmetic.

Learn: how to use the Percentage Calculator

Find the question you are asking. Each calculator is labelled in plain words.
Type the two numbers. Results and the full working update as you type.
Use the working line to check the answer by hand or to show it in homework, invoices and reports.

Features

Mode 1: what is X% of Y, for discounts, tips and tax
Mode 2: X is what percent of Y, for scores, shares and completion rates
Mode 3: percentage increase or decrease from X to Y, for prices and growth
Every result shows its formula with your numbers substituted in
Clear handling of zero and empty inputs, no NaN results

Worked example

20% of 80 is 16 (80 x 0.20). 16 is 20% of 80 (16 / 80 x 100). Going from 80 to 100 is a +25% increase ((100 - 80) / 80 x 100).

Frequently asked questions

How do I calculate a discount?

Use mode 1 for the discount amount: 30% of $120 is $36 off. The price you pay is 120 - 36 = $84. Or multiply the price by (1 - 0.30) directly.

Percentage change vs percentage points?

If a rate moves from 4% to 5%, that is a 1 percentage point rise but a 25% increase. Mode 3 gives the percent change; subtract the two rates for percentage points.

Why does mode 2 refuse zero?

"X is what percent of 0" has no answer because division by zero is undefined. The tool tells you instead of showing an error code.

Can I use decimals?

Yes, every field accepts decimals, for example 7.5% of 199.99.

How do I calculate a discount price?

Work out the discount amount (percent of the price), then subtract it. For 30% off 120: 30% of 120 is 36, so you pay 84. Mode 1 of this calculator gives the amount; the result line shows both the saving and the final price logic.

What is the difference between percent and percentage points?

Use percentage points for the arithmetic difference between two percentages: unemployment moving from 4% to 5% rose by 1 percentage point. The percent change is 25 percent, because 1 is a quarter of 4.

How do I reverse a percentage increase?

Divide by the multiplier, not by subtracting the percent. If a price of 120 includes a 20% increase, the original was 120 / 1.2 = 100. Subtracting 20% of 120 would wrongly give 96.

How do I work out what percent one number is of another without a calculator?

Divide the part by the whole, then multiply by 100. For 45 out of 60: 45 divided by 60 is 0.75, times 100 is 75 percent. The second mode of this calculator performs exactly that division and multiplication, and shows the result to two decimal places for marks, ratios and completion rates.

What is X% of Y?

X is what percent of Y?

Percentage change from X to Y

Quick answer