Calculate percentages instantly with our free online percentage calculator. Whether you need to find what percent of a number is, calculate percentage change between two values, or determine percentage difference, our tool handles it all with precision.
Our percentage calculator offers three specialized modes to cover every scenario:
**"What is X% of Y?"** - Use this to find a portion of a whole. Example: What is 20% of 150? (Answer: 30).
**"X is what % of Y?"** - Use this to find the ratio. Example: 25 is what % of 100? (Answer: 25%).
**"X increased/decreased by Y%"** - Use this for markups or markdowns.
Ideal for tracking growth or decline. If your portfolio went from $1000 to $1200, enter these values to see a 20% increase. This mode handles both positive (growth) and negative (loss) changes automatically.
Used when comparing two values where neither is the "start" or "end", like comparing the height of two buildings. It calculates the difference relative to their average.
Understanding the math behind the numbers can help you solve problems even without a calculator. Here are the core formulas:
| Goal | Formula |
|---|---|
| Find X% of Y | Value = Y × (X / 100) |
| Find what % X is of Y | Percentage = (X / Y) × 100 |
| Percentage Increase/Decrease | Diff % = ((New - Old) / Old) × 100 |
Want to impress your friends or calculate tips instantly? The secret is to break numbers down into 10% and 1% chunks.
To find 10% of any number, simply move the decimal point one place to the left.
* Example: 10% of 250 is 25.
Need 20%? Just double it (25 × 2 = 50).
Need 5%? Just halve it (25 ÷ 2 = 12.5).
To find 1%, move the decimal point two places to the left.
* Example: 1% of 250 is 2.5.
Need 3%? Multiply by 3 (2.5 × 3 = 7.5).
The term comes from the Latin per centum, meaning "by the hundred". The sign % evolved from the Italian term per cento, which was abbreviated as "p.c." and eventually morphed into the two circles with a slash we recognize today. It standardized commerce in the Roman Empire and remains the global language of business, science, and statistics.
A frequent error is confusing "percentage change" with "percentage points". If a rate goes from 10% to 15%, it rose by 5 percentage points, but the percentage increase is actually 50% (5 is half of 10). Always double-check which metric you need.
Percentages are essentially fractions in disguise (50% = 1/2). Check out our Fraction Calculator to convert between them. For more complex scientific formulations, use the Scientific Calculator. Working with probabilities? Try our Random Number Generator.