Percentage & Discount Calculator
Calculate percentages of any number, percentage change, exam scores, and discounts with sales tax in real time.
Calculate Value from Percentage
18% of 2,500 is exactly 450
Quick answer
To find X% of a number, multiply the number by X and divide by 100 (20% of 250 = 50). Percentage change = (new − old) ÷ old × 100. To reverse a percentage (find the original before a discount or tax), divide by (1 ± rate).
The five percentage formulas you actually need
- X% of Y = Y × X ÷ 100.
- X is what % of Y = X ÷ Y × 100 (exam marks: 432 of 500 = 86.4%).
- Percentage increase or decrease = (new − old) ÷ old × 100.
- Add a percentage (price plus GST, VAT or sales tax) = price × (1 + rate ÷ 100).
- Remove a percentage (original price before a 20% discount) = sale price ÷ (1 − 0.20).
Common mistakes
Percentages are not symmetric: a 50% fall followed by a 50% rise leaves you at 75% of where you started. And a “20% off, then another 10% off” deal is a 28% discount, not 30%.
Percentage points are not percent: an interest rate rising from 8% to 9% is a 1 percentage-point increase but a 12.5% relative increase.
Reference tables & worked examples
| Question | Working | Answer |
|---|---|---|
| 20% of 250 | 250 × 20 ÷ 100 | 50 |
| 432 out of 500 as % | 432 ÷ 500 × 100 | 86.4% |
| Increase from 80 to 100 | (100 − 80) ÷ 80 × 100 | +25% |
| Price ₹1,000 + 18% GST | 1,000 × 1.18 | ₹1,180 |
| Original price before 25% off (sale 750) | 750 ÷ 0.75 | 1,000 |
| 20% off, then 10% off | 0.8 × 0.9 = 0.72 | 28% total discount |
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 480 = 480 × 15 ÷ 100 = 72.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%.
How do I work out my exam percentage?
Divide marks obtained by total marks and multiply by 100. 432 out of 500 = 86.4%.
How do I remove tax from a price that includes it?
Divide by 1 plus the tax rate. A ₹1,180 price that includes 18% GST has a pre-tax value of 1,180 ÷ 1.18 = ₹1,000.
Are two successive discounts added together?
No. 20% off then 10% off equals 0.8 × 0.9 = 0.72 of the price, a 28% total discount.
What is the difference between percent and percentage points?
Percentage points measure the arithmetic difference between two percentages (8% to 9% is +1 point); percent measures relative change (+12.5%).
Estimates for general information only — not tax, legal or financial advice. Check your payslip, employer or a qualified adviser before acting.
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