How do I calculate what is X percent of a number?

Use the first calculator: enter the percentage and the number, for example 20% of 150. The tool multiplies 150 by 0.20 to give 30. The result updates instantly as you type.

How do I work out what percentage one number is of another?

Use the second calculator: enter the part and the whole, for example 45 is what percent of 180. The tool divides 45 by 180 and multiplies by 100 to give 25%.

How do I calculate a percentage increase or decrease?

Use the third calculator: enter the original value and the new value. A move from 50 to 65 is a 30% increase; a move from 80 to 60 is a 25% decrease. Increases are positive and decreases are negative.

Percentage Calculator

Three percentage calculators in one — find a percent of a number, work out what percent one value is of another, and calculate percentage increase or decrease. Perfect for discounts, tips, taxes and grades.

📖 New guide: How to Calculate a Percentage →

What is P% of a number?

Percentage (%)

Of number

—

Result

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X is what percent of Y?

Number (X)

Of total (Y)

—

X as a percentage of Y

Percentage increase / decrease

From (original)

To (new)

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Percentage change

About this percentage calculator

This free percentage calculator solves the three questions people ask most often. Use "What is P% of a number" for discounts, sales tax and tips (20% of $150 = $30). Use "X is what percent of Y" for grades, test scores and proportions (45 out of 180 = 25%). Use "percentage increase / decrease" for price changes, growth and weight loss (50 → 65 is a 30% increase). Every result updates instantly as you type and nothing is sent to a server.

Frequently asked questions

How do I calculate what is X% of a number?: Enter the percentage and the number in the first calculator — e.g. 20% of 150 gives 30.
How do I work out what percentage one number is of another?: Use the second calculator — 45 is what percent of 180 gives 25%.
How do I calculate a percentage increase or decrease?: Use the third calculator — from 50 to 65 is a 30% increase; from 80 to 60 is a 25% decrease.

Understanding the mechanics of percentages

A percentage is fundamentally a ratio expressed as a fraction of one hundred. The term originates from the Latin per centum, meaning by the hundred, which establishes the number 100 as the universal denominator for comparison. By converting disparate values into this standardized scale, you can compare parts of a whole even when the underlying totals differ significantly.

To determine a percentage, you divide the part by the whole and multiply the resulting decimal by one hundred. When calculating percentage change, the formula requires finding the difference between the new value and the original value, dividing that difference by the original value, and then converting to a percentage. This process relies on identifying the correct base value, which serves as the reference point for the entire calculation.

The most frequent error occurs when users confuse the base value in percentage increase or decrease problems. People often mistakenly divide the difference by the new value instead of the original value, which leads to mathematically incorrect results. Another common pitfall is attempting to add or subtract percentages directly without converting them to their decimal equivalents, which ignores the relationship between the percentage and the specific total being measured.