Percentage Calculator

Three Ways to Calculate a Percentage

Percentage questions usually come in one of three shapes. X% of Y finds a portion of a number (e.g. "what is 20% of 150?"). X is what % of Y finds the relationship between two numbers (e.g. "30 is what percent of 150?"). Percentage change finds how much a value has grown or shrunk between two points (e.g. "from 80 to 100 is what % increase?").

Worked examples

20% of 150: divide 20 by 100, then multiply by 150. The result is 30.

30 is what percent of 150? Divide 30 by 150, then multiply by 100. The result is 20%.

Going from 80 to 100 is a 25% increase. Reversing the inputs (100 to 80) gives a 20% decrease, because the starting value changes.

Formula / Calculation Method

X% of Y = (X ÷ 100) × Y.
X is what % of Y = (X ÷ Y) × 100.
% Change = [(New − Old) ÷ |Old|] × 100.

How to Use This Tool

Choose the tab that matches your question.
Enter the two numbers involved.
Click Calculate to see the result instantly.

Common Use Cases

Calculating tips, tax, or discounts

Working out grade or test percentages

Measuring growth or decline between two values

Everyday percentage math for school or work

Choose the correct base

For “X is what % of Y,” Y is the whole or comparison amount. Swapping the two inputs answers a different question: 30 is 20% of 150, but 150 is 500% of 30. Division by zero is undefined, so the whole cannot be zero.

Percentage points are different

A rate moving from 10% to 15% rises by 5 percentage points. Its relative increase is 50%, which is what the change tab returns when you enter 10 and 15. State which measure you mean when reporting a rate change.

Zero and negative starting values

A change from zero has no finite percentage baseline and is rejected. With a negative starting value, this tool divides by its absolute value: from −100 to −50 is reported as a 50% increase. That convention may not suit financial growth reporting across zero, so include the original values alongside the result.

Results use up to four decimal places. Keep the original inputs when a later calculation needs more precision.

Frequently Asked Questions

How do I calculate a percentage increase?

For a positive starting value, subtract old from new, divide by old, and multiply by 100. This tool uses the absolute starting value for negative inputs; see the convention above.

Can a percentage exceed 100%?

Yes. 300 is 150% of 200. A percentage above 100 means the part or comparison amount is larger than the chosen base.

Why can’t I calculate growth from zero?

The formula divides by the starting value. When that value is zero, percentage change is undefined. Report the absolute difference instead.