How this percentage calculator works
The calculator treats a percent as a value per hundred. For example, 20% is handled as 20 / 100, or 0.2, during the calculation.
Supported formulas
- Percent of a number: result = number x percent / 100
- Part as percent of whole: percent = part / whole x 100
- Percentage change: percent change = (new value - original value) / original value x 100
- Increase/decrease: result = number x (1 +/- percent / 100)
- Whole from part and percent: whole = part / (percent / 100)
Example calculation
If you want to find 20% of 150, convert 20% to 0.2 and multiply: 150 x 0.2 = 30.
Assumptions and limitations
Inputs are treated as comparable numeric values. Percentage change is undefined when the original value is zero because the formula divides by the original value. Negative original values are accepted, but the interpretation can be counterintuitive, so the calculator shows a warning.
References
- Math is Fun: Introduction to Percents - plain-language educational reference, accessed 2026-05-13.
- Calculator.net Percentage Calculator - competitor benchmark, accessed 2026-05-13.
- CalculatorSoup Percentage Calculator - competitor benchmark, accessed 2026-05-13.
- Omni Calculator Percentage Calculator - competitor benchmark, accessed 2026-05-13.
FAQ
What does percent mean?
Percent means per hundred. For example, 25% means 25 out of 100, or 0.25 as a decimal.
How do I calculate percentage change?
Subtract the original value from the new value, divide by the original value, then multiply by 100.
Why is percentage change from zero undefined?
Percentage change compares the change to the original value. If the original value is zero, the formula would require division by zero.
Last reviewed: 2026-05-13