What is A% of B?
20% of 15030
(20 ÷ 100) × 150 = 30
EVERYDAY · FREE ONLINE CALCULATOR
Percentage Calculator
Solve missing percentages, compare percentage difference, calculate increases and decreases, or reverse a discount. Explore independent tools with visible formulas and worked examples.
Detailed optionsStep-by-step guideWorked examples
01 / THE ALL-PURPOSE SOLVER
Find the missing percentage, whole or part.
Enter any two values. Leave the third blank, then calculate.
of=
Example: to find “30 is what % of 150?”, leave Percentage blank, enter Whole 150 and Part 30.
Missing result found30
(20 ÷ 100) × 150 = 30
02 / ASK IT IN YOUR OWN WORDS
Percentage calculators in common phrases.
Three frequent questions, each with its own inputs and result.
A is what % of B?
30 as a percentage of 15020%
(30 ÷ 150) × 100 = 20%
A is B% of what?
30 is 20% of150
30 ÷ (20 ÷ 100) = 150
03 / COMPARE TWO VALUES
Percentage difference calculator
Compare two nonnegative values using their average as the denominator.
- Absolute difference: |190 − 453| = 263
- Average: (190 + 453) / 2 = 321.5
- Divide the difference by the average, then multiply by 100.
Percentage difference81.804044%
|190 − 453| ÷ ((190 + 453) ÷ 2) × 100 = 81.804044%
Difference is symmetric. Change has a starting point.
From 190 to 453, percentage change is 138.421053%. Swapping A and B leaves the difference unchanged, but changes the percentage-change denominator.
04 / FOLLOW AN INCREASE OR DECREASE
Percentage change calculator
Find a new value, the original value or the percentage. Enter exactly two values.
Missing new value found120
100 × (1 + 20 ÷ 100) = 120
05 / WORK BACKWARD
Reverse percentage & discount calculator
Find the original amount when you know the final amount and the percentage change.
An 80 price after a 20% discount means 80 ÷ 0.8 = 100 originally. Adding 20% to 80 would give 96 instead.
Original value before the change100
80 ÷ (1 − 20 ÷ 100) = 100
YOUR ANIMATED GUIDE
Follow your numbers, step by step.
These steps use your current inputs. Choose a step or play the walkthrough.
STEP 1 / 4
2 known values
1234
Identify the two known values
A percentage problem connects a percentage, a whole and a part. Enter any two and leave exactly one blank.
20% of 150 = ?
Explore at your own pace
How to use this percentage calculator
Percent means “per hundred.” This page provides separate calculators for finding a percentage, finding the whole, comparing two values, measuring change and reversing an increase or discount. Start with the missing-value solver, use a familiar wording in the common-phrases section, or jump directly to difference and change. Each tool shows the numbers substituted into its formula so the result is easier to check.
What is a percentage?
A percentage expresses a ratio relative to 100. For example, 25% is 25/100, 0.25 or one quarter. To take 25% of 80, multiply 80 by 0.25 to get 20. Values over 100% are valid: 150% of 80 is 120. A percentage can describe a share, a rate or a change, so the wording of the question determines which formula to use.
Percentage difference versus percentage change
Percentage difference compares two nonnegative values without choosing an original value. It divides their absolute difference by their average. Percentage change chooses an original value and divides the signed change by that original. Swapping the values leaves percentage difference unchanged, but changes a percentage-change result. The two calculations answer different questions and should not be used interchangeably.
Discounts, increases and reversing a change
To decrease a price by 20%, multiply by 0.8. To reverse that discount from the final price, divide by 0.8. Adding 20% to the discounted price does not restore the original: 100 reduced by 20% is 80, and 80 increased by 20% is 96. Successive changes multiply rather than add; two 10% discounts leave 81% of the original amount.
Percentage points and relative change
A rate moving from 20% to 25% rises by 5 percentage points. Relative to the original 20%, that is a 25% increase: (25 − 20) / 20 × 100. Use percentage points to describe the direct gap between rates and percentage change to describe how large that gap is relative to the starting rate.
Percentage formulas, explained
Find the part
Part = (percentage ÷ 100) × whole
Example: 20% of 150 = 0.20 × 150 = 30.
Find the percentage or the whole
Percentage = part ÷ whole × 100; whole = part ÷ (percentage ÷ 100)
A zero denominator cannot determine a unique answer.
Percentage difference
Difference % = |A − B| ÷ ((A + B) ÷ 2) × 100
Used here for nonnegative inputs. Both zero is undefined because their average is zero.
Percentage change
Change % = (new − original) ÷ original × 100
A positive result indicates an increase for a positive original value; a negative result indicates a decrease.
Increase, decrease and reverse
New = original × (1 ± p/100); original = new ÷ (1 ± p/100)
Reversing a 100% decrease is undefined: every original becomes zero.
PUT THE FORMULA TO WORK
Worked examples you can try.
Load an example into the calculator, then change one value to explore.
Find a share
20% of 150 = 30. Use the solver with percentage 20 and whole 150, leaving the result empty.
Compare 190 and 453
The absolute difference is 263 and their average is 321.5. Percentage difference = 263 / 321.5 × 100 ≈ 81.804%.
Reverse a 20% discount
An item costs 80 after a 20% discount. Its original price was 80 / 0.8 = 100.
MAKE THE NUMBERS MAKE SENSE
Common mistakes to avoid
- Dividing by the new value when the question asks for change from the original.
- Adding percentage changes that should be multiplied.
- Confusing a five-percentage-point rise with a five-percent relative increase.
A LITTLE MORE CLARITY
Frequently asked questions
How do I calculate a percentage increase?
Subtract the original value from the new value, divide by the original value, then multiply by 100. A negative result indicates a decrease.
Can I calculate with a zero original value?
A percentage of zero is zero. A ratio or percentage change with a zero denominator is undefined, so the calculator asks for a nonzero original value.
Can I enter values above 100%?
Yes. A percentage of a number can exceed 100%. For example, 200% of 30 equals 60.
Why are percentage change and percentage difference different?
Change uses the original value as its denominator. Difference uses the average of two values and has no preferred starting value.
How do I find the price before a discount?
Divide the discounted price by 1 minus the discount rate as a decimal. For an 80 price after a 20% discount, calculate 80 / 0.8 = 100.
What happens with zero or negative values?
Zero denominators are rejected. The symmetric difference tool uses nonnegative values. Other tools allow signed values, but percentage change from a negative original can require careful interpretation.
How are answers rounded?
The tools calculate using JavaScript floating-point numbers and show up to six decimal places. Small rounding differences can occur for repeating decimals.
Methodology & assumptions
Calculations run in your browser using the formulas and assumptions explained on this page. Intermediate values retain full floating-point precision; displayed amounts are rounded. Percentage tools use the displayed denominator and reject undefined divisions. Sharing an input link places those inputs in the URL.