How the percentage calculator works
"Percent" means "per hundred," so 15% is 15 out of every 100, or 0.15. Nearly every percentage question is a rearrangement of one simple relationship: part = percent × whole. Choose the question you want answered, enter the two numbers, and the calculator applies the right version of the formula and explains the result in plain English.
The formulas
- A% of B: result = A ÷ 100 × B.
- A is what percent of B: result = A ÷ B × 100.
- Percent change from A to B: result = (B − A) ÷ |A| × 100. A positive result is an increase, a negative one a decrease.
Examples
15% of 200 is 30. 50 is 25% of 200. Going from 80 to 100 is a 25% increase, but going from 100 back to 80 is a 20% decrease. That asymmetry surprises many people: percentage changes are always measured against the starting value, so the same gap of 20 is a bigger share of 80 than of 100.
Everyday uses
Percentages show up in discounts, tips, tax rates, grades, interest rates and investment returns. When a price is cut by 25% and later raised by 25%, it does not return to where it started; it ends 6.25% lower, because the increase is applied to a smaller number. For differences between interest rates or tax rates, use "percentage points" — going from 4% to 5% is a 1 percentage point increase, but a 25% relative increase.
Frequently asked questions
How do I find a percentage of a number?
Convert the percentage to a decimal and multiply. For 20% of 80, multiply 0.20 by 80 to get 16.
How do I calculate a percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100.
What is the difference between percent and percentage points?
Percentage points measure the simple difference between two percentages. Percent change measures that difference relative to the starting percentage.
Can a percentage be more than 100?
Yes. If a value more than doubles, the increase is over 100%, and a part can be more than 100% of a smaller whole.
Results are estimates for educational purposes only and are not financial, tax, legal or medical advice. See our disclaimer. Last reviewed 2026-10-22.