Percentage Calculator
Six common percentage calculations in one place — updated live as you type.
What is X% of Y?
X is what percent of Y?
Percentage increase / decrease (From → To)
Value increased/decreased by a percentage
Reverse percentage (find the original value)
Percentage difference between two numbers
Percentage difference is symmetric and has no "starting" value — it divides the gap between A and B by their average, so it's the right formula for comparing two measurements rather than tracking a change over time. That's different from percentage change above, which is directional: going from 80 to 100 is a +25% change, but going from 100 to 80 is a -20% change, even though the percentage difference between 80 and 100 is the same either way (about 22.22%).
How to Calculate a Percentage
- To find a percentage of a number, enter the percent and the base number in the "What is X% of Y?" section — the result updates as you type.
- To find what percent one number is of another, enter both numbers in the "X is what percent of Y?" section.
- To measure a percentage change, enter the starting ("From") and ending ("To") values in the third section.
- To apply a percent increase or decrease to a value, use the "Value increased/decreased by a percentage" section and pick a direction.
- To work backward and find the original value before a percent change was applied, use the "Reverse percentage" section.
- To compare two values without treating either one as the "starting point," use the "Percentage difference" section instead of the increase/decrease calculator.
- Read the result directly below each section — no button click needed, everything is live.
Frequently Asked Questions
What's the difference between the six calculators on this page?
They cover the six most common percentage questions: finding a portion of a number (20% of 150), finding what percent one number is of another (30 is what % of 150), finding the percent change between two values (going from 80 to 100), applying a percent increase or decrease to a value (100 decreased by 20%), reversing a percent change to find the original value (a value that is 80 after a 20% decrease), and finding the percentage difference between two values with no starting point (80 versus 100).
Why does the percentage increase/decrease calculator use the absolute value of From?
The tool divides the change by the absolute value of the starting number so that a negative starting value doesn't flip the sign of the result — this keeps increase and decrease meaning what you'd expect even when your starting number is negative.
Why is my result blank?
Each calculator only shows a result once its required fields contain valid numbers; if you leave a field empty, or a required divisor like Y, From, an average of two values, or (1 plus/minus percent/100) works out to zero, the result box stays empty since that math is undefined.
How many decimal places does the calculator show?
Results are shown to up to 4 decimal places using locale-aware number formatting, so you get more precision than a typical whole-number percentage answer.
Can this tool calculate percentage change for a value that goes down?
Yes — if To is smaller than From, the tool automatically labels the result a decrease and shows the percentage drop, rather than a negative increase.
How do I calculate the result after a percentage increase or decrease?
Use the 'Value increased/decreased by a percentage' calculator: enter the starting value, the percent, and choose increase or decrease. Increasing multiplies the value by (1 + percent/100), and decreasing multiplies it by (1 - percent/100) — for example, 100 decreased by 20% equals 80.
What does the reverse percentage calculator do?
It works backward from a result to find the original value before a percentage change was applied. If a final value came from an increase, the tool divides by (1 + percent/100); if it came from a decrease, it divides by (1 - percent/100) — for example, a value that is 80 after a 20% decrease had an original value of 100.
What's the difference between percentage difference and percentage change?
Percentage change compares a starting value to an ending value and is directional, using (new minus old) divided by old — going from 80 to 100 is a 25% increase, but going from 100 to 80 is a 20% decrease. Percentage difference compares two values with no starting point, using the absolute difference divided by their average, so it gives the same result regardless of order — the percentage difference between 80 and 100 is about 22.22%.