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Percentage Calculator
Percent of a number, proportion, and percent change, step by step.
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Percentage Calculator Online
Percent of a number, proportion, and percent change, step by step.
Solve the Three Percentage Problems Everyone Asks
Pick one of the three everyday percentage questions, enter the numbers, and press Run. The result comes with the formula that was used and a plain-English sentence explaining it, so you can check the working instead of trusting a black box. There is no account, no watermark and nothing to install.
What Is X% of Y?
This is the "percent of" mode. The percentage is divided by 100 and multiplied by the value, shown as (X ÷ 100) × Y. Asking for 15% of 2,400 gives (15 ÷ 100) × 2400 = 360. It is the mode you want for discounts, commission, tax, tips and VAT.
X Is What Percent of Y?
This is the reverse question. The part is divided by the whole and multiplied by 100, shown as (X ÷ Y) × 100. If 30 is what percent of 150, the answer is 20%. Note the tool refuses a base of zero here, because there is no meaningful percentage of nothing.
Percentage Increase and Decrease
Enter a starting value A and a new value B to get the change as a percentage. The change is B − A, divided by the absolute value of A and multiplied by 100, and the result is labelled an increase or a decrease. Going from 100 to 125 is a 25% increase; from 125 back to 100 is a 20% decrease. Those two numbers differ because each uses its own starting point — a detail worth knowing before you quote a figure.
Decimals, Negatives and Division by Zero
All fields accept decimals, and the results are trimmed of meaningless trailing zeros. Negative values are rejected where a percentage of a negative amount would be ambiguous, a start value of zero is refused with a clear message rather than a division error, and a base of zero is refused in the reverse mode. You get an explanation either way instead of a blank result.
Why the Formula Is Shown
Most percentage mistakes come from dividing by the wrong number — the new total instead of the original, for instance. Every result here prints the exact expression used alongside the result, which makes it obvious which number was the base. It also means you can paste the same working into a spreadsheet or a report and get identical numbers.
Frequently asked questions
How do I find 15% of a number?
Choose "What is X% of Y?", put 15 in the percentage field and the number in the value field, then press Run. The answer is 0.15 times your number: 15% of 2400 is 360.
What is the difference between percent change and a percentage of a value?
A percentage of a value answers "what is X% of Y". Percent change compares two points in time: enter the old value and the new value and the tool divides the difference by the old value, then labels the direction as an increase or a decrease.
How do I calculate a percentage increase from A to B?
Use the "Percentage increase/decrease" mode with A as the starting value and B as the new value. The result is (B − A) ÷ |A| × 100, reported with the formula and the direction.
Why is my 20% increase not the reverse of a 20% decrease?
Because each percentage is measured against its own starting point. After a 20% increase, the new total is 1.2 times the original, so dropping back requires a 20 ÷ 120 = 16.7% decrease to return to where you started.
What happens if I enter zero as the starting value?
The tool refuses the calculation and explains that percent change from zero is undefined, because the change would have to be divided by zero. Start from a non-zero value and the same calculation works normally.
Does this calculator show its working?
Yes. Every mode returns the formula in plain notation — for example (15 ÷ 100) × 2400 — plus a sentence such as "15% of 2400 is 360", so you can verify the result yourself.
About this tool
Percentage Calculator solves the three most common percentage problems: X% of Y, X is what percent of Y, and the percentage increase or decrease from A to B.
How to use: pick a mode, enter the values, then press Run to see the result and formula.
- Shows the working formula
- Handles decimals and negatives
- Covers percent-of, proportion and change