Math
Percentage Calculator
Solve common percentage problems in either direction: find a percent of a number, convert part to percent, measure percent change, find the missing whole, or reverse a percent increase or decrease.
Result
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- Difference
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- Multiplier
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Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What this percentage calculator can solve
| Mode | Use it when | Formula |
|---|---|---|
| X% of Y | You know the percent and the whole | part = percent / 100 x whole |
| X is what % of Y | You know the part and whole | percent = part / whole x 100 |
| % change | You compare an old value to a new value | change% = (new - old) / old x 100 |
| Find whole | You know the part and percent | whole = part / (percent / 100) |
| Reverse change | You know the final value after a percent change | original = final / (1 + change% / 100) |
Percent versus percentage points
Percent is relative. Percentage points are absolute. Moving from 10% to 15% is a 5 percentage-point increase, but the relative percent increase is 50%.
Mental percentage shortcuts
- 10% means move the decimal one place left.
- 5% is half of 10%.
- 1% is one hundredth of the whole.
- 15% can be done as 10% plus 5%.
Worked examples
20% of 150
Find a part from a percent and whole
Result
30
9 is what % of 45
Convert part to percent
Result
20%
80 to 100
Measure percent change
Result
25%
12 is 15% of what?
Find the missing whole
Result
80
After 20% increase, final is 120
Find the original value
Result
100
Frequently asked questions
How do I calculate a percentage of a number?+
Convert the percent to a decimal by dividing by 100, then multiply by the whole. For example, 15% of 200 is 0.15 x 200 = 30.
How do I reverse a percentage increase?+
Divide the final value by 1 plus the percent change as a decimal. If 120 is after a 20% increase, the original was 120 / 1.20 = 100.
Why is percent change from zero undefined?+
Percent change divides by the original value. If the original value is zero, that division is not defined.
Can percentages be over 100?+
Yes. 150% means 1.5 times the whole. Percent change can also exceed 100% when the new value more than doubles.
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Last updated: May 8, 2026