Percentage Calculator

What this calculator does

Percentages make comparisons easier by expressing values out of 100. This calculator covers the most common percentage questions in one place.

Formula used

For X percent of Y, multiply Y by X divided by 100. For percentage change, subtract the old value from the new value, divide by the old value and multiply by 100.

How to read the result

Be careful with reverse percentages and percentage change. A 20 percent fall followed by a 20 percent rise does not return to the original value because the second percentage is based on a smaller number.

Assumptions

• Uses decimal arithmetic in the browser.
• Reverse percentage treats Y as the final value after X percent was added.

Sources and checks

This calculator uses a standard public formula. Where rules or thresholds can change, source links are listed on the relevant page.

Frequently asked questions