Percentage Calculator
Three everyday percentage questions, answered as you type: a percent of a number, what percent one number is of another, and the percentage change between two values.
Reviewed by the CalcCafe editorial team · Last updated 1 July 2026 · How we test our tools
Example
20% of 250 is 50. 45 is 25% of 180. And going from 120 to 150 is a +25% change.
How it works
Percent of a number is (X ÷ 100) × Y. 'X is what percent of Y' is (X ÷ Y) × 100. Percentage change is ((new − old) ÷ old) × 100, where a negative result means a decrease.
Good to know
This Percentage Calculator bundles the three percentage problems people actually run into into one live tool: finding a percent of a number (like 20% of 250), working out what percent one number is of another (45 out of 180), and measuring the percentage change between an old and a new value (120 up to 150). Results update as you type, so it suits shoppers checking discounts, students checking homework, and anyone comparing two figures without reaching for a formula.
Reach for the right box depending on your question. Use the first when you know the rate and the base and want the resulting amount, such as a tip, tax, or sale discount. Use the second when you have a part and a whole and want the ratio as a percentage, like a test score or a completion rate. Use the third when you have a before-and-after pair and want the relative growth or drop, such as a price hike or a year-over-year change.
Read the change box by its sign: a positive number means the value grew, and a negative number means it fell relative to the starting figure. Note that this is the percentage change from the original, not a percentage point difference. Going from 4% to 6% is a +50% change, not "+2%" — keep that distinction in mind when you are already working with values that are themselves percentages.
One practical caveat: percentage increases and decreases are not symmetric. A value that drops 50% needs to rise 100% to get back to where it started, because the second calculation uses the smaller number as its base. When you reverse a change, switch the old and new values rather than reusing the same percentage.
Frequently asked questions
How do I find what percent one number is of another?
Use the middle box: divide the part by the whole and multiply by 100. For example, 45 out of 180 is 25%.
How is percentage increase calculated?
Subtract the old value from the new value, divide by the old value, then multiply by 100. From 120 to 150 is (30 ÷ 120) × 100 = 25%.
Can it show a percentage decrease?
Yes — if the second value is lower than the first, the change box shows a negative percentage.
Is my data uploaded anywhere?
No. Everything is calculated in your browser with JavaScript — nothing is sent to a server, so it's private and works offline once loaded.
Is this calculator free?
Yes, completely free with no sign-up and no limits.
People also ask
How do I add a percentage to a number?
Calculate the percent of the number, then add it to the original. For example, adding 8% to 250 is 250 + (8% of 250) = 250 + 20 = 270.
What is the difference between percentage and percentage points?
A percentage change is relative to the starting value, while a percentage point is the plain arithmetic difference between two percentages. Moving from 10% to 15% is a rise of 5 percentage points but a 50% increase.
How do I calculate a discount price?
Find the discount amount as a percent of the original price, then subtract it. A 30% discount on $80 removes $24, leaving $56.
How do I reverse a percentage to find the original number?
Divide the final amount by 1 plus the rate (as a decimal) for an increase, or by 1 minus the rate for a decrease. If 120 is the result after a 20% increase, the original was 120 ÷ 1.20 = 100.
Why isn't a 50% drop reversed by a 50% gain?
Each calculation uses its own starting value as the base, and the base shrinks after a decrease. A 50% drop from 100 gives 50, and recovering to 100 from 50 requires a 100% increase.
How do I turn a fraction or decimal into a percentage?
Multiply a decimal by 100, or divide the top of a fraction by the bottom and multiply by 100. So 0.25 is 25%, and 3/4 is (3 ÷ 4) × 100 = 75%.
Does this percentage calculator work offline?
Yes. It runs entirely in your browser with JavaScript, so once the page has loaded it keeps working without an internet connection.
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Sources & references
These tools follow our methodology and provide educational estimates only — verify important figures with a qualified professional.