Percentage Calculator - Free Online Tool

How This Tool Works

The Percentage Calculator solves six common percentage problems without requiring you to remember formulas. It calculates what percentage one number is of another (e.g. 45 is what % of 180?), finds a percentage of a given number (e.g. 15% of 340), calculates percentage increase or decrease between two values, reverses a percentage change to find the original value, and computes the percentage difference between two numbers. Percentages are fundamental to finance, statistics, academic scoring, and everyday decisions — this tool removes the mental arithmetic barrier.

How to Use

Select the calculation type using the tabs or mode selector.
Enter value A (typically the part or the new value) and value B (the whole or the original value).
Click Run. The result shows the answer along with the formula used.
For percentage change: A is the new value, B is the old value. A positive result means increase; negative means decrease.

Common Questions

What is the difference between percentage change and percentage difference?

Percentage change measures how a value changed over time (old→new) and has a direction (increase or decrease). Percentage difference compares two values with no time component and uses their average as the base — it is always positive.

Why does a 50% increase followed by a 50% decrease not return to the original?

Because each percentage applies to a different base. Start with 100: +50% gives 150, then −50% of 150 gives 75. The net result is a 25% loss from the original. Percentage movements are multiplicative, not additive.

How do I find the original price before a discount?

If an item costs $63 after a 30% discount, the original price is $63 ÷ (1 − 0.30) = $90. Use the 'reverse percentage' mode in this calculator.

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