How to use the Percentage Calculator
- Find the question that matches yours. Each box answers one common percentage question — read the sentence in the box and fill in the blanks.
- Type your numbers. The answer appears as soon as both values are filled in. Commas in large numbers (like 1,250) are fine.
- Check the working. Under each answer the formula is shown with your numbers plugged in, so you can copy the method into homework, a report or a spreadsheet.
What this calculator does
"Percent" simply means "per hundred", so every percentage question is really a question about a fraction of 100. The trouble is that the same few numbers can be combined in several different ways, and choosing the wrong formula is the most common source of mistakes. This page separates the five questions people ask most often:
- What is X% of Y? — for tips, tax, commission, and "how much is 20% of this?"
- X is what percent of Y? — for test scores, progress towards a goal, and shares of a total.
- Percentage increase or decrease — for price changes, growth rates, and before-and-after comparisons.
- Increase or decrease a number by X% — for pay rises, price mark-ups and reductions.
- Percentage difference — for comparing two values when neither one is the obvious starting point.
How the formulas work
Percentage of a number
result = Y × X ÷ 100
15% of 240 is 240 × 15 ÷ 100 = 36. A handy shortcut: percentages are reversible, so 15% of 240 is the same as 240% of 15. If one version is easier to do in your head, use that one.
What percent one number is of another
percentage = X ÷ Y × 100
If you scored 36 out of 40 on a test, 36 ÷ 40 × 100 = 90%. Always divide the part by the whole.
Percentage change
change % = (new − original) ÷ original × 100
A price that rises from 80 to 100 has increased by (100 − 80) ÷ 80 × 100 = 25%. If it then falls back from 100 to 80, that is a decrease of (80 − 100) ÷ 100 × 100 = −20%. The two percentages are different because the starting point is different — one of the most useful ideas to remember about percentages. When the original value is negative, the calculator divides by its absolute value so the sign of the answer still shows the direction of change; if the original value is zero, a percentage change cannot be calculated.
Increasing or decreasing by a percentage
result = Y × (1 + X ÷ 100) or Y × (1 − X ÷ 100)
A salary of 2,500 increased by 12% becomes 2,500 × 1.12 = 2,800.
Percentage difference
difference % = |X − Y| ÷ ((X + Y) ÷ 2) × 100
Percentage difference compares two values against their average, so the answer is the same whichever order you enter them. The difference between 40 and 60 is 20 ÷ 50 × 100 = 40%. Use this when comparing two measurements, two stores' prices or two survey results — and use percentage change when there is a clear "before" and "after".
Real-world examples
| Situation | Question type | Working | Answer |
|---|---|---|---|
| Restaurant tip of 18% on a 65.00 bill | X% of Y | 65 × 18 ÷ 100 | 11.70 |
| 42 correct answers out of 50 | X is what % of Y | 42 ÷ 50 × 100 | 84% |
| Rent rose from 900 to 945 | Percentage change | (945 − 900) ÷ 900 × 100 | +5% |
| Website visitors fell from 12,000 to 9,000 | Percentage change | (9,000 − 12,000) ÷ 12,000 × 100 | −25% |
| Add 8% sales tax to 49.99 | Increase by X% | 49.99 × 1.08 | 53.99 |
Common mistakes to avoid
- Dividing by the wrong number. For a percentage change, always divide by the original (starting) value, not the new one.
- Adding percentages that apply one after another. A 10% rise followed by a 10% fall does not return to the start: 100 → 110 → 99. The second 10% is taken from a bigger number.
- Confusing percent with percentage points. If an interest rate moves from 4% to 5%, it has risen by one percentage point, but by 25 percent.
- Reversing a discount by adding the same percentage back. After 20% off, a price of 80 needs a 25% increase — not 20% — to return to 100.
Tips
- Shopping? The Discount Calculator handles sale prices, savings, sales tax and stacked discounts in one step.
- For time-based percentages — such as what share of a year has passed — first find the number of days with the Date Difference Calculator, then use "X is what percent of Y".
- Converting measurements before comparing them? Use the Unit Converter so both values are in the same unit.
For a step-by-step explanation with more worked examples, read How to Calculate Percentage: Simple Methods, Examples, and Formulas.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 30% of 150 is 150 × 30 ÷ 100 = 45.
How do I work out a percentage increase?
Subtract the original value from the new value, divide by the original value, and multiply by 100. From 50 to 65 is (65 − 50) ÷ 50 × 100 = 30%.
What is the difference between percentage change and percentage difference?
Percentage change measures movement from a starting value to a new value, so the order matters. Percentage difference compares two values against their average, so the order does not matter.
Why can a percentage be more than 100%?
Because the part can be larger than the whole you are comparing it to. If sales grow from 100 to 250, that is a 150% increase, and 250 is 250% of the original.
How many decimal places are shown?
Results are rounded to at most four decimal places for display, with trailing zeros removed. The working uses full precision.
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