Percentage Calculator

How this percentage calculator works

This tool handles the three percentage questions people search for most: finding a percentage of a number, figuring out what percent one number is of another, and calculating the percentage change between two values. Switch tabs above to use whichever mode you need.

The three percentage formulas

X% of Y: Result = (X ÷ 100) × Y
X is what % of Y: Result = (X ÷ Y) × 100
Percentage change from X to Y: Result = ((Y − X) ÷ X) × 100

Step-by-step: how to calculate a percentage by hand

Decide which of the three questions you’re answering (of, is-what-percent, or change).
Convert any percentage into a decimal by dividing by 100 (15% becomes 0.15).
Multiply or divide according to the matching formula above.
If you’re calculating percentage change, remember a negative result means a decrease.

Worked examples

X% of Y: What is 15% of 200? (15 ÷ 100) × 200 = 0.15 × 200 = 30.

X is what % of Y: 30 is what percent of 200? (30 ÷ 200) × 100 = 0.15 × 100 = 15%.

Percentage change: A price rises from $80 to $100. ((100 − 80) ÷ 80) × 100 = (20 ÷ 80) × 100 = +25%.

Common percentage mistakes

Using the wrong base number for percentage change. Always divide by the original (starting) value, not the new one.
Confusing percentage points with percent. Going from 20% to 25% is a 5 percentage-point increase, but a 25% relative increase.
Forgetting to convert to a decimal before multiplying, which inflates results by 100x.
Averaging percentages incorrectly when the underlying totals differ (a simple average of two percentage rates isn’t valid unless the sample sizes are equal).

Tips for working with percentages

To quickly estimate 10% of any number, move the decimal point one place left.
To find 15%, take 10% and add half of that amount.
A percentage change over 100% means the new value is more than double the original.
When comparing discounts, apply consecutive percentage discounts one at a time, not by adding the percentages together.

How do I calculate a percentage increase or decrease?

Subtract the original value from the new value, divide by the original value, then multiply by 100. A positive result is an increase; a negative result is a decrease.

What’s the difference between percent and percentage points?

Percentage points measure the raw difference between two percentages (25% − 20% = 5 percentage points). Percent measures the relative change (a 20% to 25% move is a 25% relative increase, since 5 ÷ 20 = 0.25).

How do I reverse a percentage calculation to find the original number?

If you know that X is a certain percent of an unknown number, divide X by that percentage (as a decimal). For example, if 30 is 15% of a number, the number is 30 ÷ 0.15 = 200.

Can percentages be negative or over 100%?

Yes. A percentage change can be negative (a decrease) and can exceed 100% when a value more than doubles. A percentage of a whole (like a share of a total) is normally between 0% and 100%.