Percentage Calculator
Three percentage calculations in one tool. Find X% of a number, express a value as a percentage, or calculate percentage increase and decrease — instantly, with no formula needed.
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How Percentage Calculator Works
What Is a Percentage?
A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin per centum, meaning "per hundred." Percentages are used in everyday life for discounts, tax rates, exam scores, interest rates, tips, and much more.
Our Percentage Calculator handles the three most common percentage questions in a single tool — no formula memorisation required.
Calculation Types
1. What is X% of Y? (Percentage of a Number)
Use this when you want to find a portion of a number.
Formula: Result = (X ÷ 100) × Y
Example: What is 20% of 350?
Result = (20 ÷ 100) × 350 = 0.20 × 350 = 70
Common uses: calculating a 20% tip on a restaurant bill, finding the VAT amount on a price, working out a discount on a sale item.
2. X is What Percent of Y? (Value as a Percentage)
Use this when you want to express one number as a percentage of another.
Formula: Result = (X ÷ Y) × 100
Example: 45 is what percent of 180?
Result = (45 ÷ 180) × 100 = 0.25 × 100 = 25%
Common uses: calculating your exam score as a percentage, finding what share of a budget is spent on a particular category, expressing a part-to-whole relationship.
3. Percentage Change (Increase or Decrease)
Use this when comparing two values to find by how much one has grown or shrunk relative to the original.
Formula: Change = ((New − Original) ÷ Original) × 100
Example: A price rises from £80 to £100.
Change = ((100 − 80) ÷ 80) × 100 = (20 ÷ 80) × 100 = 25% increase
Common uses: calculating price inflation, measuring investment returns, comparing month-over-month metrics, finding the percentage of weight lost or gained.
Percentage Increase vs Percentage Decrease
The same percentage change formula works for both increases and decreases. A positive result means an increase; a negative result means a decrease. Our calculator labels the direction automatically.
| Original | New | Change | Direction |
|---|---|---|---|
| 100 | 125 | 25% | Increase |
| 100 | 75 | 25% | Decrease |
| 200 | 200 | 0% | No Change |
| 50 | 100 | 100% | Increase (doubled) |
Common Percentage Shortcuts
Memorising a few shortcuts can help you estimate percentages mentally:
- 10% — Move the decimal point one place left (10% of 250 = 25)
- 5% — Half of 10% (5% of 250 = 12.5)
- 1% — Move the decimal point two places left (1% of 250 = 2.5)
- 25% — Divide by 4 (25% of 80 = 20)
- 50% — Divide by 2 (50% of 80 = 40)
Accuracy & Sources
Last reviewed: July 2026. Formula source: Standard arithmetic percentage formulas. All calculations run in your browser. No data is sent to any server.
Frequently Asked Questions
There are three common percentage formulas: (1) To find X% of Y: multiply Y by X and divide by 100. Example: 15% of 200 = (15 × 200) ÷ 100 = 30. (2) To find what percentage X is of Y: divide X by Y and multiply by 100. Example: 30 is what % of 200? = (30 ÷ 200) × 100 = 15%. (3) Percentage change from X to Y: divide (Y minus X) by X and multiply by 100. Our calculator handles all three automatically.
Use the Percentage Change tab. Enter the original value and the new (higher) value. The formula is: ((New Value - Original Value) ÷ Original Value) × 100. For example, if a price increases from £80 to £100: ((100 - 80) ÷ 80) × 100 = 25% increase. A positive result always means an increase.
Use the same Percentage Change tab as for an increase — the formula is identical. Enter the original (higher) value and the new (lower) value. For example, if a price drops from £100 to £75: ((75 - 100) ÷ 100) × 100 = -25%, meaning a 25% decrease. Our calculator labels the direction automatically.
A percentage point is an absolute difference between two percentages. If interest rates rise from 3% to 5%, that is a 2 percentage point increase — but it is also a 66.7% increase in the rate itself. Confusing these two is a common error. Use percentage points when comparing rates or proportions directly; use percentage change when expressing growth relative to a base.
To find 20% of any number quickly: divide by 10 to get 10%, then multiply by 2. For example, 20% of 350: 350 ÷ 10 = 35, then 35 × 2 = 70. Alternatively, enter the values into the 'What is X% of Y?' tab above and click Calculate.
Yes. A percentage can exceed 100% when a value is more than the base. For example, if sales grow from 50 units to 150 units, that is a 200% increase. Our calculator handles values above 100% correctly for all three calculation types.
Tax calculations use the 'What is X% of Y?' formula. To find the GST amount on a pre-tax price, enter the tax rate as the percentage and the pre-tax price as the number. For example, 18% GST on ₹1,000: 18% of 1000 = ₹180 GST, so the total is ₹1,180. For more specific GST calculations, use our dedicated GST Calculator.