Percentage Calculator
Percentages appear everywhere - discounts, tax rates, profit margins, test scores, survey results, and price changes - and the calculation you need shifts depending on what you are trying to find. This calculator covers the three most common percentage questions in one place: what is X% of a number, what percentage is one number of another, and what is the percentage change between two values. Results are instant; no formula recall required.
How to use this tool
- 1Choose the type of calculation at the top: 'percentage of a number', 'what percent A is of B', or 'percentage change'.
- 2Enter the required numbers in the fields. The result updates instantly as you type.
- 3For percentage change, a positive result means an increase and a negative result means a decrease.
- 4Use the reset button to clear the fields and start a new calculation.
Formula used
Example
Choose 'percentage of a number', enter 20 and 150. The result is 30. Used to calculate a 20% tip on a 150 dinner, a 20% commission on a sale, or a 20% down payment.
Choose 'percentage change', enter 80 as the old value and 100 as the new value. The result is a 25% increase. Note: a move from 100 back to 80 is a 20% decrease, not 25% - increases and decreases are not symmetrical.
Common use cases
- Calculating a tip: find 15% or 20% of a restaurant bill
- Working out a commission: find what 8% of 4,500 in monthly sales amounts to
- Checking a price change: entering old and new prices to see the percentage increase
- Finding a student's score as a percentage: 43 correct out of 50 = 86%
- Splitting a bill: finding what share 35 is of a total 140
Common mistakes
- Using 'percentage of a number' when you want percentage change - if a price moved from 80 to 100, use the percentage change mode, not 'percentage of a number'.
- Putting the new value in the old field for percentage change - the original or starting value always goes in the first field.
- Assuming percentage increase and decrease are symmetrical - a 50% drop followed by a 50% rise returns to only 75% of the original value, not 100%.
- Confusing percentage points with percentages - if a rate goes from 4% to 6%, it increased by 2 percentage points but by 50% as a percentage change.
Frequently asked questions
How do I find a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 20% of 150 is (20 / 100) x 150 = 30. The calculator does this automatically in 'percentage of a number' mode.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, then multiply by 100. A move from 80 to 100 is ((100 - 80) / 80) x 100 = 25% increase. Use 'percentage change' mode.
What is the difference between percentage and percentage points?
Percentage points measure the absolute difference between two percentages. If an interest rate goes from 3% to 5%, it rose by 2 percentage points, but by 67% as a percentage change. The terms are often confused in financial and political reporting.
How do I calculate a percentage discount?
Use 'percentage of a number' to find the discount amount, then subtract from the original price. For a 25% discount on 80: 25% of 80 is 20, so the final price is 60. Or use the Discount Calculator which does this in one step.
Why is a 50% drop followed by a 50% rise not back to the original?
Because each percentage is calculated on a different base. If 100 drops by 50%, it becomes 50. Then 50% of 50 is 25, so it rises to 75 - not back to 100. The base changes after each step.
How do I find what percentage one number is of another?
Use 'what percent A is of B' mode. Divide A by B and multiply by 100. For example, 35 out of 50 is (35 / 50) x 100 = 70%. Useful for test scores, survey results, and share calculations.
Is this calculator accurate for large numbers?
Yes. The calculator uses standard floating-point arithmetic and rounds results to two decimal places. For very large numbers or high-precision financial work, verify with a spreadsheet.
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