Percentage Calculator
Calculate percentages, percentage increases, decreases, and differences instantly.
All calculations happen locally in your browser — nothing is uploaded, stored or tracked.
Pick a mode
Choose percent of a number, increase/decrease or percentage difference.
Enter your values
Type in the numbers you want to work with.
Get the answer
The result appears instantly, with the decimal equivalent too.
What Is a Percentage Calculator?
A percentage calculator solves the three everyday percentage problems people meet in shops, schools and spreadsheets: finding a percentage of a number, measuring a percentage increase or decrease between two values, and comparing two numbers as a percentage difference. Percent means "per hundred", so every calculation is simply a matter of scaling a number by a fraction of 100.
The calculator has three modes. Percent of a number answers questions like "what is 15% of 240?". Increase or decrease compares two values and reports the change as a percentage, which is how price rises, salary changes and exam score improvements are usually quoted. Percentage difference compares two values symmetrically against their average, the standard way to compare measurements.
The Percentage Formula
The first formula gives you the size of a percentage share of a number. The second tells you how much a value has moved relative to where it started. The third compares two values without favouring either one as the reference point.
Example Calculation
A jacket costs $80 and is marked up to $96. The percentage increase is (96 − 80) ÷ 80 × 100 = 20%. Using percent-of mode, 15% of 240 is 240 × 0.15 = 36. For a percentage difference, compare 50 and 60: |50 − 60| ÷ 55 × 100 ≈ 18.2%.
Common Mistakes
- Confusing percentage increase with percentage difference — increase uses the starting value as the base, difference uses the average.
- Forgetting that a 100% increase doubles the original value, while a 100% decrease reduces it to zero.
- Adding percentages without a common base: a 10% rise followed by a 10% fall is not back to the original price.
Your data never leaves your device.
Every calculation on this site runs in your browser using vanilla JavaScript. Nothing is uploaded, stored or tracked.
- 100% local, client-side calculations
- No data stored on any server
- No tracking, no analytics, no ads scripts
- Works offline once loaded
Frequently Asked Questions
How do I calculate a percentage of a number?
Multiply the number by the percentage divided by 100. For example, 20% of 150 = 150 × 20 ÷ 100 = 30.
What is the formula for percentage increase?
Percentage increase = (new value − original value) ÷ original value × 100. If the result is negative, it is a percentage decrease.
How is percentage difference different from percentage change?
Percentage change divides by the starting value, so it depends on direction. Percentage difference divides by the average of the two values, so it is the same either way round.
What is 10% of 50?
5. Multiply 50 by 0.10 — ten percent of any number is simply the number divided by ten.
Can I calculate percentage decrease with this tool?
Yes. Enter the original value and the new (lower) value in the increase/decrease mode; the result shows as a negative change or decrease.
How do I add a percentage to a price?
Multiply the price by (1 + percentage ÷ 100). Adding 8% to $50 gives 50 × 1.08 = $54.