Percentage Calculator
Answer the six most common percentage questions: what is X% of a number, what percent one number is of another, what a number is a percentage of, the change between two values, the difference between two values, and a value after an increase or decrease. Fill in an equation and calculate.
How to use this calculator
- Pick the equation that matches your question — the three are independent, so use whichever one fits.
- Fill in the two numbers. Each equation reads like a sentence, so the fields sit where the words go.
- Press Calculate. After the first result, editing either number updates the answer live.
- For a percentage change, the tool also states the direction in words — increase, decrease or no change — so the sign is never ambiguous.
The three percentage formulas
Almost every percentage question is one of these three. Each solves for a different unknown:
- Percentage of a number: value × (percent ÷ 100). The share of a total.
- What percent A is of B: (A ÷ B) × 100. The relationship between a part and a whole.
- Percentage change: ((new − old) ÷ old) × 100. Growth or shrinkage against a starting point (the tool divides by the absolute value of the start, so it needs a starting value above zero).
A worked example
Follow the calculator's own default numbers through all three equations. Ask what is 15% of 200: multiply 200 × (15 ÷ 100) = 30. Ask 50 is what percent of 200: divide 50 ÷ 200 = 0.25, then × 100 = 25%. Ask the change from 80 to 100: (100 − 80) ÷ 80 = 0.25, so a 25% increase.
Increases and decreases are not symmetric
Reversing a percentage does not use the same percentage. Going from 80 up to 100 is a 25% increase, but going from 100 back down to 80 is only a 20% decrease — the base changed from 80 to 100, so the same 20-unit gap is a smaller share. A price cut of 20% followed by a 20% rise never returns you to where you started.
Reverse percentages: finding the original
When you know the price after a discount and want the original, divide rather than add the percentage back. A jacket costing $60 after 25% off was 60 ÷ (1 − 0.25) = 60 ÷ 0.75 = $80 before the sale. The same move strips a known tax rate out of a gross total. There is no dedicated reverse mode here, but the arithmetic is a single division.
Percentage points vs. percent
This trips people up constantly. If an interest rate goes from 10% to 15%, it rose 5 percentage points — but that is a 50% increase relative to where it started. Use "percentage points" for the raw gap between two percentages, and "percent" for change measured against the original value.
Decimals, fractions and percentages
They are three ways to write the same thing: 0.25 = 25% = 1/4. Multiply a decimal by 100 to get a percentage, or divide a percentage by 100 to get a decimal. To turn a fraction into a percentage, divide it out first. For fraction arithmetic itself, use the fraction calculator; for a tip or discount at the checkout, the tip calculator and sales tax calculator apply the same math.
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Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 200 is 200 × 15 ÷ 100 = 30. The first tool above does this for you.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 out of 200 is (30 ÷ 200) × 100 = 15%.
How do I calculate percentage increase or decrease?
Subtract the old value from the new value, divide by the old value, and multiply by 100. Going from 200 to 250 is ((250 − 200) ÷ 200) × 100 = 25% increase. A negative result means a decrease.
How do I convert a decimal or fraction to a percentage?
Multiply a decimal by 100 (0.25 → 25%). For a fraction, divide the top by the bottom first, then multiply by 100 (1/4 → 0.25 → 25%). To go the other way, divide the percentage by 100.
What is the difference between a percent and a percentage point?
They are not the same. If a rate rises from 10% to 15%, that is a 5 percentage-point increase but a 50% relative increase (5 ÷ 10). Percentage points measure the gap between two percentages; percent measures the change relative to the starting value.
How do I find the original price before a discount?
Divide the final price by (1 − discount as a decimal). A jacket costing $60 after 25% off was 60 ÷ 0.75 = $80 originally. This "reverse percentage" is the same idea as removing sales tax from a total.
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About this calculator
Method reviewed for accuracy on July 18, 2026
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