Percentage Calculator
Calculate percentages four ways — X% of Y, what %, change, and difference
“What is 17.5% of 849?” “43 is what percent of 215?” “Revenue went from $12,400 to $15,100 — what is the percentage increase?” These are three different percentage questions that each require a different formula. Instead of remembering which formula to use, pick the mode that matches your question.
Four Calculation Modes
Mode 1: What is X% of Y?
Calculates a percentage of a given value. The formula: result = (X / 100) × Y
Examples:
- What is 15% of 200? → 30
- What is 8.25% of $1,499.99? → $123.75 (sales tax)
- What is 20% of 350? → 70 (tip calculation)
Mode 2: X is what % of Y?
Finds what percentage one number is of another. The formula: result = (X / Y) × 100
Examples:
- 43 is what % of 215? → 20%
- 7 is what % of 28? → 25%
- 156 is what % of 1,200? → 13%
Mode 3: Percentage Change (Increase/Decrease)
Calculates the percentage change from an old value to a new value. The formula: result = ((new - old) / old) × 100
Examples:
- From 200 to 250 → +25% increase
- From 500 to 425 → −15% decrease
- From $12,400 to $15,100 → +21.77% increase
Mode 4: Percentage Difference
Calculates the relative difference between two values without a “before/after” relationship. The formula: result = (|A - B| / ((A + B) / 2)) × 100
Examples:
- Difference between 100 and 120 → 18.18%
- Difference between 45 and 55 → 20%
When to Use Change vs. Difference
Percentage change has a direction: from old to new. “Revenue grew 25%” means revenue increased relative to its previous value. The old value is the reference point.
Percentage difference is symmetric: neither value is “before” or “after.” Use it when comparing two independent measurements — for example, “Server A handles 450 req/s and Server B handles 520 req/s; the percentage difference is 14.4%.”
Precision and Rounding
The calculator displays results with up to 4 decimal places by default. You can adjust the precision for your use case. Financial calculations often require exactly 2 decimal places; scientific calculations may need 6 or more.
Common Percentage Reference
| Fraction | Percentage | Decimal |
|---|---|---|
| 1/2 | 50% | 0.5 |
| 1/3 | 33.33% | 0.3333 |
| 1/4 | 25% | 0.25 |
| 1/5 | 20% | 0.2 |
| 1/8 | 12.5% | 0.125 |
| 1/10 | 10% | 0.1 |
| 1/100 | 1% | 0.01 |
Privacy
All calculations run entirely in your browser. No numbers or results are transmitted to any server.
Frequently Asked Questions
How do I calculate a percentage increase? Use Mode 3 (Percentage Change). Enter the original value and the new value. The tool calculates ((new - old) / old) x 100. A positive result is an increase; negative is a decrease.
What is the difference between percentage change and percentage difference? Percentage change measures the shift from an old value to a new value (directional). Percentage difference measures the relative gap between two values without implying a before/after relationship (symmetric).
Can I use decimal percentages like 8.25%? Yes. All modes accept decimal inputs. This is useful for tax rates, interest rates, and precise scientific calculations.
How do I reverse a percentage? If 150 is 30% of X, what is X? Divide: X = 150 / 0.30 = 500. Mode 1 can verify this: 30% of 500 = 150.
Is my data sent to a server? No. All calculations happen entirely in your browser. No data is transmitted anywhere.