Percentage Calculator
Four everyday percentage questions, each with its own calculator. Pick the one that matches your question and the working is shown with the answer.
How percentages work
"Percent" means "per hundred", so 15% is 15 out of every 100, or 0.15 as a decimal. Every percentage question is a version of one relationship between three numbers:
Part = Percentage ÷ 100 × Whole
Each calculator above solves that relationship for a different unknown:
- P% of a number: Part = P ÷ 100 × Whole. 15% of 80 = 0.15 × 80 = 12.
- What percent X is of Y: Percentage = X ÷ Y × 100. 12 out of 48 = 0.25 × 100 = 25%.
- X is P% of what: Whole = X ÷ (P ÷ 100). If 30 is 25% of a total, the total is 30 ÷ 0.25 = 120.
- Adding or subtracting P%: New value = Value × (1 ± P ÷ 100). 200 increased by 10% = 200 × 1.10 = 220.
Worked example: a pay rise
Your salary is 2,400 a month and you receive a 4% raise. The raise is 4 ÷ 100 × 2,400 = 96, and the new salary is 2,400 × 1.04 = 2,496. If you later learn a colleague earns 2,600, you are paid 2,496 ÷ 2,600 × 100 = 96% of their salary.
Mistakes to avoid
Percentage increases and decreases do not cancel out
A 20% rise followed by a 20% fall does not return you to the start. 100 × 1.20 = 120, then 120 × 0.80 = 96. The fall is taken from a larger number. To undo a 20% increase you need a decrease of 20 ÷ 120 ≈ 16.67%.
Removing a percentage that was already added
If a price of 120 already includes 20% tax, the pre-tax price is 120 ÷ 1.20 = 100, not 120 − 20% = 96. Use the "X is P% of what number" calculator with X = 120 and P = 120.
Percent versus percentage points
An interest rate moving from 3% to 4% has risen by 1 percentage point, but by 33.3% in relative terms. The percentage change calculator explains the difference in detail.
Common questions
How do I find 10% of a number in my head?
Divide by 10 by moving the decimal point one place left: 10% of 350 is 35. From there, 5% is half of that (17.5) and 20% is double it (70).
Is X% of Y the same as Y% of X?
Yes. 8% of 50 and 50% of 8 are both 4, because both equal 8 × 50 ÷ 100. Swap the numbers whenever one version is easier to do mentally.
Can a percentage be more than 100?
Yes. 150% of 40 is 60, and a value that grows from 40 to 100 has increased by 150%. Only a share of a whole (such as a test score) is limited to 100%.
How are decimals and separators handled?
You can type 12.5 or 12,5. A number such as 1,500 is read as fifteen hundred, and the calculator tells you when it has read a comma that way. Results use a period as the decimal point.