Percentage Calculator
Calculator
What is X% of Y?
X% of Y
12
X is what percent of Y?
X ÷ Y × 100
15%
Percentage change
From an old value to a new value
15% · increase
Percentage difference
Between two values (order doesn't matter)
40%
Add or subtract a percent
Base ± percent
plus 92 · minus 68
X is P% of what?
X ÷ (P ÷ 100)
50
About this calculator
This calculator handles six common percentage tasks in one place: finding what X% of a number is, figuring out what percentage one number is of another, finding the original number when you know X is P% of it, calculating the percentage change between two values, measuring the percentage difference between two values, and adding or subtracting a percentage from a base number. Type into any card and the answer updates instantly.
How to read your results
The page is split into six independent mode cards, each solving a different percentage question. Each card shows two input fields and displays its result — or a short note if the inputs are incomplete or mathematically impossible — directly below the fields. All six modes work simultaneously, so you can use as many at once as you like.
How it's calculated
Each mode uses a direct formula. "What is X% of Y" computes (X / 100) × Y. "X is what % of Y" computes (X / Y) × 100, requiring Y ≠ 0. "X is P% of what" solves for the base as X / (P / 100), requiring P ≠ 0. Percentage change is ((new − old) / |old|) × 100, signed, requiring the old value ≠ 0. Percentage difference is |A − B| / ((|A| + |B|) / 2) × 100, order-independent, requiring the two values not both be zero. "Add / subtract a percent" gives base × (1 + p / 100) and base × (1 − p / 100). Every mode is a rearrangement of the single rule-of-three proportion part / whole = percent / 100. All formulas follow standard mathematical definitions as documented on MathIsFun.
Worked example
Enter 15 in the percent field and 80 in the number field of the "What is X% of Y" card. In the "Add / subtract a percent" card, enter 80 as the base and 15 as the percent.
15% of 80 is 12. Adding 15% to 80 gives 92, and subtracting 15% from 80 gives 68 — confirming all three results are consistent.
| Percent | Decimal | Fraction |
|---|---|---|
| 1% | 0.01 | 1/100 |
| 5% | 0.05 | 1/20 |
| 10% | 0.1 | 1/10 |
| 12.5% | 0.125 | 1/8 |
| 20% | 0.2 | 1/5 |
| 25% | 0.25 | 1/4 |
| 33 1/3% | 0.333… | 1/3 |
| 50% | 0.5 | 1/2 |
| 66 2/3% | 0.666… | 2/3 |
| 75% | 0.75 | 3/4 |
| 100% | 1 | 1/1 |
| Number | 5% | 10% | 15% | 20% | 25% | 50% |
|---|---|---|---|---|---|---|
| 20 | 1 | 2 | 3 | 4 | 5 | 10 |
| 40 | 2 | 4 | 6 | 8 | 10 | 20 |
| 50 | 2.5 | 5 | 7.5 | 10 | 12.5 | 25 |
| 80 | 4 | 8 | 12 | 16 | 20 | 40 |
| 100 | 5 | 10 | 15 | 20 | 25 | 50 |
| 150 | 7.5 | 15 | 22.5 | 30 | 37.5 | 75 |
| 200 | 10 | 20 | 30 | 40 | 50 | 100 |
| 250 | 12.5 | 25 | 37.5 | 50 | 62.5 | 125 |
| 300 | 15 | 30 | 45 | 60 | 75 | 150 |
| 500 | 25 | 50 | 75 | 100 | 125 | 250 |
Frequently asked questions
What is the difference between percentage change and percentage difference?
Percentage change measures a directional shift from an old value to a new one: ((new − old) / |old|) × 100. It has a sign — positive for an increase, negative for a decrease. Percentage difference, by contrast, is order-independent: it divides the absolute gap by the average of the two values, giving a symmetric measure that does not imply direction.
Why does the "X is what % of Y" card refuse to calculate when Y is zero?
The formula is (X / Y) × 100. Division by zero is undefined, so the calculator shows a note rather than an error or an infinite result. Make sure the denominator is a non-zero value.
Can I use these formulas for discounts, tips, or tax?
Yes. To find a discount amount, use "What is X% of Y" with X as the discount rate and Y as the original price. To find the price after a percentage off or on, use "Add / subtract a percent." The same logic applies to tips, VAT, or any markup.
How do I calculate X% of Y?
Multiply the whole by the percentage written as a decimal: Y × (X / 100). For example, 20% of 50 is 50 × 0.20 = 10. The "What is X% of Y" card does this for any two numbers.
How do I find a percentage increase or decrease?
Subtract the old value from the new one, divide by the old value, and multiply by 100: ((new − old) / old) × 100. Going from 100 to 125 is a 25% increase; going from 50 to 40 is a 20% decrease. A positive result is an increase, a negative one a decrease.
X is what percent of Y?
Divide the part by the whole and multiply by 100: (X / Y) × 100. For example, 12 is 15% of 80 because 12 / 80 = 0.15. Use the "X is what % of Y" card, keeping the whole (Y) non-zero.
X is P% of what number?
Divide the part by the percentage written as a decimal: X / (P / 100). For example, 25 is 50% of 50 because 25 / 0.50 = 50, and 15 is 30% of 50 because 15 / 0.30 = 50. Use the "X is P% of what" card, keeping the percent (P) non-zero so the base is defined.
How do I use the rule of three to calculate a percentage?
The rule of three treats a percentage problem as a proportion: part / whole = percent / 100. Write down the three values you know, cross-multiply, and divide by the remaining known value. To find what percent 12 is of 80: 12 × 100 / 80 = 15%. To find 15% of 80: 15 × 80 / 100 = 12. And if 15% of a number is 12, the number is 12 × 100 / 15 = 80. Every card on this page is a special case of that one proportion.
How do I calculate a percentage without a calculator?
Anchor on 10% by moving the decimal point one place to the left: 10% of 240 is 24. From there, 5% is half of that (12), 20% is double (48), and 1% is 2.4. Combine the anchors to build any percentage: 15% of 240 is 24 + 12 = 36. It also helps to remember that 25% is a quarter and 50% is a half.
How do I convert a fraction or a decimal to a percentage?
Multiply by 100 and add the percent sign. The decimal 0.35 is 35%, and 1.25 is 125%. For a fraction, divide first: 3/8 = 0.375 = 37.5%. To go the other way, divide the percentage by 100: 42% = 0.42.
Popular scenarios
Sources
- Ch. 6 Introduction to Percents - Prealgebra 2e — OpenStax
- Percentage — Wikipedia
- Relative change — Wikipedia
- Cross-multiplication — Wikipedia
Reviewed by the YouCalc Team · Last reviewed
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