Percentage Calculator

Three calculators in one — find a percentage of a number, work out what percent one value is of another, or measure the change between two numbers. Results update as you type.

🔒 100% private — nothing is uploaded, runs entirely in your browser
What is % of ?
Enter both values to see the result.

How the percentage calculator works

Pick a mode, type your numbers, and the answer appears instantly — no button to press, no page reload.

1

X% of Y

Find part of a whole — like a 20% tip on a $150 bill, or 15% off a price. Formula: (X ÷ 100) × Y.

2

X is what % of Y

Turn a ratio into a percentage — like a test score of 30 out of 150. Formula: (X ÷ Y) × 100.

3

Increase / decrease

Measure change between two numbers — a price rise, a discount, a growth rate. Formula: ((To − From) ÷ From) × 100.

Percentage basics

A percentage is just a number expressed as a fraction of 100 — "per cent" literally means "per hundred". So 25% is the same as 25/100, or 0.25. To take a percentage of a number, convert the percent to a decimal and multiply.

Percentage change compares a new value against an original one. A positive result is an increase, a negative result is a decrease. Note that a 50% rise followed by a 50% fall does not return you to the start — because each change is measured against a different base.

This calculator handles decimals and negative numbers, and shows a clear message instead of an error when a value is missing or when a division by zero would occur.

🔒

Private by design. Every calculation runs right here in your browser with plain JavaScript. Your numbers are never uploaded, saved or sent anywhere — we never see them.

Frequently Asked Questions

What can this percentage calculator work out? ▼
It has three modes: X% of Y (a percentage of a number), X is what % of Y (turning one number into a percentage of another), and % increase / decrease (the change between two values). Switch modes with the tabs at the top.
How do I find X% of a number? ▼
Convert the percentage to a decimal and multiply: the formula is (X ÷ 100) × Y. For example, 20% of 150 is (20 ÷ 100) × 150 = 30 — handy for a tip, a discount or tax.
How do I work out what percent one number is of another? ▼
Divide the part by the whole and multiply by 100: (X ÷ Y) × 100. For example, a score of 30 out of 150 is (30 ÷ 150) × 100 = 20%.
How is percentage increase or decrease calculated? ▼
The formula is ((To − From) ÷ From) × 100. A positive result is an increase and a negative one a decrease — for example from 120 to 150 is a 25% increase.
Why doesn't a 50% rise then a 50% fall return to the start? ▼
Because each change is measured against a different base. A 50% rise on 100 gives 150; a 50% fall is then taken off 150, removing 75 to leave 75 — not the original 100. Percentage changes don't simply cancel out.

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