Percentage Calculator
Three common modes: find a percentage, find a share, and calculate percent change — covering almost every everyday percentage need.
About This Tool
A percentage expresses one number as a fraction of another out of 100, using the % symbol. In essence, percentages convert the ratio of two quantities into a form with a denominator of 100, making them easy to compare and express.
This tool offers the three most common percentage modes:
- Find a percentage: calculate what B% of A equals — e.g. 15% of 200 is 30. Commonly used for discount prices, tips, taxes and more.
- Find a share: calculate what percent A is of B — e.g. 45 is 75% of 60. Commonly used for completion rates, score rates and market share statistics.
- Find percent change: calculate the percentage increase or decrease from A to B — e.g. rising from 80 to 100 is a 25% increase. Commonly used for price movements, period-over-period performance and population growth analysis.
Please note: in percent-change calculations, if A (the original value) is negative or zero, the percentage change is undefined or ambiguous — use the absolute change instead.
How to Use
- Click one of the three calculation modes above according to your needs.
- The input labels change automatically with the mode — enter two values as prompted.
- Click "Calculate" to see the result and the corresponding formula.
FAQ
Why doesn't a percentage increase followed by a decrease return to the original value?
Because the base of each calculation differs. For example, 100 increased by 20% gives 120; decreasing 120 by 20% gives 96, not 100 — by then the base has already become 120.
Does growing 100% mean doubling?
Yes. Growing 100% means an increase of 100%, e.g. 50 growing by 100% becomes 100; growing 200% makes it three times the original.
In "A is what percent of B", can B be 0?
No. The denominator of a share calculation cannot be zero — dividing by 0 is mathematically undefined, and the tool will prompt you to fix your input.
How do I use this tool for discounts?
Use the "What is B% of A" mode: enter the original price as A and the percentage you pay as B. For example, for a 299 item at 20% off (you pay 80%), "80% of 299" gives 239.2.
How do I convert between percentages and decimals?
Divide a percentage by 100 to get a decimal (15% = 0.15); multiply a decimal by 100 and add the % sign to get a percentage (0.25 = 25%). You can also use the "A is what percent of B" mode to convert.