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X% of Y
X is what % of Y
Percentage Change
Three Percentage Calculators in One
This free percentage calculator answers the three questions people ask most about percentages: what is X% of a number, what percent is one number of another, and how much did a value increase or decrease. Each calculator above has its own two fields, and the answer appears as soon as both are filled in.
The arithmetic runs in your browser as you type, so nothing is uploaded and there is no limit on how many calculations you run. For other everyday math, browse the full set of free online calculators.
How to Use the Percentage Calculator
- 1
Pick the calculator that matches your question
Use "X% of Y" to find a percentage of a number, "X is what % of Y" to turn a part and a total into a percentage, or "Percentage Change" to compare an old value with a new one.
- 2
Enter the two numbers
Fill in both fields of that calculator. Decimals and negative numbers are accepted.
- 3
Read the result
The answer appears as soon as both fields are filled and updates as you type, rounded to at most two decimal places.
- 4
Use the other calculators as needed
The three calculators are independent, so numbers entered in one stay in place while you work in another.
Percentage Formulas With Worked Examples
X% of Y
Result = (X ÷ 100) × Y. To find 15% of 80, multiply 0.15 by 80 to get 12. This is the calculation behind most price math: a 25% discount on an $80 item is $20 off, leaving $60, which the discount calculator works out along with your savings. Adding 8% sales tax to a $45 purchase is 0.08 × 45 = $3.60, and the sales tax calculator handles state rates and reverse calculations for you.
X is what % of Y
Percent = (part ÷ total) × 100. If you scored 42 out of 50 on a test, that is 42 ÷ 50 × 100 = 84%. When several assignments carry different weights, a simple percentage is not enough; the grade calculator combines weighted scores and shows what you need on the final.
Percentage change
Change = (new − old) ÷ old × 100. Rent that rises from $1,200 to $1,320 has gone up (1,320 − 1,200) ÷ 1,200 × 100 = 10%. A positive result is labeled Percentage Increase, a negative one Percentage Decrease (shown as a positive number, so 100 to 80 reads as a 20% decrease), and no difference reads No Change.
Why the Base Value Matters
Every percentage is measured against a base, and swapping the base changes the answer. A price that goes from 80 to 100 rose 25%, but falling from 100 back to 80 is only a 20% drop. For the same reason, a 10% rise followed by a 10% fall does not return you to where you started: 100 becomes 110, then 99, a net 1% decrease. Enter From 100 and To 99 in the Percentage Change calculator to confirm it.
Growth compounds the same way. Two years of 5% growth on 100 gives 105 and then 110.25, a total change of 10.25%, not 10%. For savings and investments over many years, the compound interest calculator applies this repeatedly with regular contributions.
Percentage vs. Percentage Point
When two figures are already percentages, their plain difference is measured in percentage points. An interest rate moving from 4% to 5% has risen by 1 percentage point, yet the rate itself is 25% higher, because (5 − 4) ÷ 4 × 100 = 25. Enter From 4 and To 5 in the Percentage Change calculator to see the relative figure. News reports and loan offers often mix these up, so check which one is meant before comparing rates on a mortgage or other loan.
This calculator measures change relative to the From value only. It does not compute the symmetric “percent difference” that divides by the average of both numbers, and it has no reverse-percentage mode; to recover an original price after 20% off, divide the sale price by 0.80 (for example, $64 ÷ 0.80 = $80).
Common uses
- Working out a discount, markup, or tax amount on a price
- Turning a test score or survey count into a percentage
- Measuring month-over-month or year-over-year growth in sales, traffic, or prices
- Checking a pay rise or rent increase as a percentage
- Applying fixed rates such as 2.5% with the zakat calculator or a 150% time-and-a-half rate with the overtime calculator
Percentage terms explained
| Term | What it means here |
|---|---|
| Percent (%) | A number expressed as parts per hundred; 20% means 20 out of every 100, or 0.20 as a decimal |
| Part | The portion you are measuring, such as the points you scored or the amount spent |
| Total (whole) | The full amount the part is compared against; it is the 100% reference |
| Percentage change | How much a value rose or fell, measured relative to its starting ("From") value |
| Percentage point | The plain difference between two percentages; 4% to 5% is a 1 percentage point rise |
| Base value | The number a percentage is calculated from; changing the base changes the answer |
Frequently Asked Questions
Divide the percentage by 100 and multiply by the number: result = (X ÷ 100) × Y. For example, 20% of 150 is 0.20 × 150 = 30. Enter 20 and 150 in the "X% of Y" calculator to get the same answer instantly.
Divide the part by the total and multiply by 100: percent = (part ÷ total) × 100. For example, 30 out of 150 is 30 ÷ 150 × 100 = 20%. Use the "X is what % of Y" calculator with Part 30 and Total 150.
Subtract the old value from the new value, divide by the old value, and multiply by 100: change = (new − old) ÷ old × 100. Going from 80 to 100 is (100 − 80) ÷ 80 × 100 = a 25% increase.
Use the same percentage change formula; the result is simply negative. Going from 100 to 80 is (80 − 100) ÷ 100 × 100 = −20%. The calculator labels this as a Percentage Decrease of 20% rather than showing a minus sign.
Because each percentage is measured from a different starting value. 80 rising to 100 is a 25% increase (measured from 80), but 100 falling back to 80 is only a 20% decrease (measured from 100). The base value always matters.
A percentage point is the simple difference between two percentages, while a percentage change is relative. If an interest rate rises from 4% to 5%, that is a 1 percentage point increase but a 25% increase in the rate itself, since (5 − 4) ÷ 4 × 100 = 25.
Divide the final number by (1 − the percentage as a decimal). If a price is $64 after 20% off, the original was 64 ÷ 0.80 = $80. The calculator has no dedicated reverse mode, but you can check the answer in "X% of Y": 80% of 80 is 64.
Yes. All fields accept decimals and negative numbers. For percentage change with a negative starting value, the change is measured against the size of that value, so going from -50 to -25 reads as a 50% increase, and a note explains this.
A result only shows once both fields of a calculator are filled in. "X is what % of Y" also needs a total other than zero, and "Percentage Change" needs a starting value other than zero, because dividing by zero has no answer; the calculator shows a message explaining this.
Results are rounded to at most two decimal places for display. For example, 1 out of 3 shows as 33.33%.
No. All three calculations run in your browser as you type, and nothing you enter is sent to a server.
Yes. It is free to use, with no signup and no limit on how many calculations you run.
Reviewed by Raja Jahangir · Last reviewed: September 30, 2026
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How do you calculate a percentage?
To find a percentage of a number, multiply the number by the percentage and divide by 100: 20% of 250 is 250 × 20 ÷ 100 = 50. To find what percentage one number is of another, divide the first by the second and multiply by 100.