Percentage Calculator — X% of Y, What %, and % Change

How to calculate percentages

Choose the calculation type using the tabs at the top, then enter your numbers. The result updates instantly as you type — no button to press.

The formula panel below the result shows exactly how the answer was calculated, so you can double-check the maths or explain it to someone else.

Three modes are available: 'X% of Y' finds a percentage of a number (e.g. 15% of 340 = 51); 'X is what % of Y' expresses one number as a fraction of another; '% change' calculates the increase or decrease between two values.

Frequently asked questions

How do I find 15% of 340?

Select the 'X% of Y' tab, enter 15 in the first field and 340 in the second. The result (51) appears immediately, along with the formula: 15 ÷ 100 × 340 = 51.

How do I calculate a percentage increase or decrease?

Select the '% change from X to Y' tab. Enter the starting value in X and the ending value in Y. A positive result means an increase; a negative result (shown with ▼) means a decrease.

What does 'X is what % of Y' mean?

This mode tells you what fraction of Y the number X represents, expressed as a percentage. For example, 51 is what % of 340? Answer: 15%. The formula is (X ÷ Y) × 100.

Is my data sent to a server?

No. All calculations happen entirely in your browser using JavaScript arithmetic. No data is uploaded or stored.

Why does the percentage change show ▲ or ▼?

The arrows indicate direction at a glance: ▲ means the value increased, ▼ means it decreased. This is especially useful when comparing figures in reports or spreadsheets.