How do I calculate a percentage by hand?

Divide the part by the whole, then multiply by 100. (35 ÷ 200) × 100 = 17.5%. The same identity in reverse gives you a portion: (17.5 ÷ 100) × 200 = 35.

What's the difference between percent change and percent difference?

Percent change has a direction — it's signed and uses the starting value as the base. Percent difference is unsigned and uses the average of the two values as the base. This calculator computes percent change.

Why does the answer for '0 is what % of 0' show a dash?

Division by zero is undefined. The calculator surfaces a dash rather than displaying Infinity or NaN.

Can I enter decimals?

Yes. Anything JavaScript's number parser accepts will work — "12.5", "-3.7", "0.001".

Does the calculator store my data?

No. Every computation happens in your browser; nothing is sent to a server.

How do I compute a percentage increase?

Use the "% change" tab. A positive result is an increase, a negative result is a decrease. From 100 to 130 is +30%; from 130 to 100 is about −23%, not −30%.

Percentage Calculator

Three percentage questions, one widget. The formula shows alongside the answer.

Percentages are everywhere — tax rates, discounts, school grades, tip amounts, scientific reporting. The three modes below cover virtually every percent question that comes up in daily life: finding a percentage of a number, expressing one number as a percentage of another, and reporting a signed percent change. Every calculation runs in your browser and the formula is shown underneath so you can verify by hand.

Find a percentage of a number

Percent (%)

Of value

35% of 200

(35 ÷ 100) × 200 = 70

How to use

Pick the question type
Tabs across the top: "What is X% of Y?", "X is what % of Y?", and "% change". Pick the one that matches the question you have.
Fill in the two numbers
The result and the formula update as you type. There is no submit button.
Read the answer
The big tinted number is the answer. The mono-spaced line under it shows exactly how the answer was computed.

Worked examples

Question	Inputs	Answer
What is 20% of 150?	20, 150	30
35 is what % of 200?	35, 200	17.5%
% change from 50 to 75	50, 75	+50%
% change from 80 to 60	80, 60	−25%

Frequently asked questions

How do I calculate a percentage by hand?: Divide the part by the whole, then multiply by 100. (35 ÷ 200) × 100 = 17.5%. The same identity in reverse gives you a portion: (17.5 ÷ 100) × 200 = 35.
What's the difference between percent change and percent difference?: Percent change has a direction — it's signed and uses the starting value as the base. Percent difference is unsigned and uses the average of the two values as the base. This calculator computes percent change.
Why does the answer for '0 is what % of 0' show a dash?: Division by zero is undefined. The calculator surfaces a dash rather than displaying Infinity or NaN.
Can I enter decimals?: Yes. Anything JavaScript's number parser accepts will work — "12.5", "-3.7", "0.001".
Does the calculator store my data?: No. Every computation happens in your browser; nothing is sent to a server.
How do I compute a percentage increase?: Use the "% change" tab. A positive result is an increase, a negative result is a decrease. From 100 to 130 is +30%; from 130 to 100 is about −23%, not −30%.

About

Why three modes?

Most online calculators bury all three operations behind a single confusing form. Splitting them up labels the question explicitly so there's no ambiguity about which number is the base and which is the part.

Rounding behaviour

Results display with up to six decimal places, with trailing zeros trimmed. The raw IEEE 754 double is used for the underlying computation, so the displayed digits are exactly what JavaScript would produce for the same operation.