Percentage Calculator
Three everyday percentage problems, one tool: find a percentage of a number, work out what percent one number is of another, or measure the percentage change between two values.
Percentages are just fractions with a denominator of 100. To find a percentage of a number, convert the percentage to a decimal by dividing by 100, then multiply. To find what percent one number is of another, divide the part by the whole and multiply by 100.
Percentage change compares a new value to a starting value: subtract the start from the new value, divide by the absolute starting value, and multiply by 100. A positive result is an increase; a negative result is a decrease.
Worked examples
Sales tax on a purchase
What is 7% of $85? Convert 7% to 0.07 and multiply by 85.
→ $5.95
Test score
You answered 42 of 50 questions correctly. 42 ÷ 50 × 100 gives your score.
→ 84%
Price increase
Gas rises from $3.20 to $3.68 per gallon. (3.68 − 3.20) ÷ 3.20 × 100.
→ 15% increase
How to Calculate Percentages
A percentage expresses a number as a fraction of 100. This free percentage calculator handles the three most common percentage problems, but understanding the math behind each one makes the results easier to trust. Here is how each method works, with a simple example for every case.
1. Find a percentage of a number
Convert the percentage to a decimal by dividing it by 100, then multiply by the number. This is the method behind sales tax, tips, and discounts.
Example: What is 15% of 200? (15 ÷ 100) × 200 = 0.15 × 200 = 30.
2. Find what percentage one number is of another
Divide the part by the whole, then multiply by 100. Use this to turn test scores, survey results, or survey responses into a percentage.
Example: 30 is what percent of 150? (30 ÷ 150) × 100 = 0.20 × 100 = 20%.
3. Calculate percentage increase or decrease
Subtract the starting value from the new value, divide by the absolute starting value, and multiply by 100. A positive result is an increase; a negative result is a decrease.
Example: Percentage increase from 80 to 100? ((100 − 80) ÷ 80) × 100 = (20 ÷ 80) × 100 = 25%.
Prefer to skip the manual math? The online percentage calculator above applies every formula instantly — just pick a mode, enter your two numbers, and read the result.
Frequently Asked Questions
How do I calculate a percentage of a number?
Convert the percentage to a decimal by dividing it by 100, then multiply by the number. For example, 15% of 200 equals (15 ÷ 100) × 200 = 30.
How do I find what percentage one number is of another?
Divide the part by the whole, then multiply by 100. For example, 30 out of 150 is (30 ÷ 150) × 100 = 20%.
How do I calculate percentage increase?
Subtract the starting value from the new value, divide by the absolute starting value, and multiply by 100. From 80 to 100, that is ((100 − 80) ÷ 80) × 100 = 25% increase.
How do I calculate percentage decrease?
Use the same change formula: ((New − Start) ÷ |Start|) × 100. A negative result means a decrease. For example, dropping from 100 to 80 is ((80 − 100) ÷ 100) × 100 = −20%, a 20% decrease.
Is this online percentage calculator free?
Yes. This is a free percentage calculator with no sign-up, no ads in the way of the results, and no limits on how many times you use it. It runs entirely in your browser.