Percentage calculator
A percentage is the part divided by the whole, times 100. Pick a mode above: X is what % of Y (an exam mark), what is X% of Y (a discount) or % change from X to Y (a pay rise). The answer appears with a sentence explaining it.
How to use the percentage calculator
- Choose the calculation with the three buttons at the top.
- Enter the two numbers: part and whole, percent and number, or old and new value.
- Read the result and its sentence, e.g. “25 is 12.5% of 200”.
- Change either number to try other scenarios.
The three percentage formulas
| Question | Formula | Example |
|---|---|---|
| X is what % of Y? | X ÷ Y × 100 | 45 of 50 = 90% |
| What is X% of Y? | Y × X ÷ 100 | 20% of 350 = 70 |
| % change X → Y | (Y − X) ÷ X × 100 | 8,000 → 8,600 = +7.5% |
Discounts, original prices and stacked discounts
450Saudi riyal with 30% off: discount 450 × 0.30 = 135Saudi riyal; price 315Saudi riyal (or 450 × 0.70).
- Original price: divide the sale price by (1 − discount): 315 ÷ 0.70 = 450.
- Stacked discounts don't add up: 20% then 10% is 28% off, because 0.80 × 0.90 = 0.72.
- Up then down: +25% then −25% turns 100 into 93.75, not 100.
Saudi shelf prices include 15% VAT; see the VAT calculator.
Exam marks and pay rises
37 out of 40 = 37 ÷ 40 × 100 = 92.5%. A salary rising from 8,000Saudi riyal to 8,600Saudi riyal is (600 ÷ 8,000) × 100 = 7.5%.
For university admission scores use the weighted percentage calculator; for university grades the GPA calculator.
Percentages in Excel
- X as a % of Y: =A1/B1, formatted as a percentage.
- X% of Y: =B1*A1%
- % change: =(B1-A1)/A1
- Price after discount: =A1*(1-B1%)
Mental shortcuts
- 10%: move the decimal point one place: 10% of 640 = 64.
- 5%: half of 10% = 32. 15%: 10% + 5% = 96.
- 1%: move two places (6.4), then multiply.
- Swap trick: 8% of 50 = 50% of 8 = 4.
Percent vs percentage point: a rate going from 4% to 5% is one percentage point, but a 25% increase in the rate itself, which matters when comparing loan offers.
Percentage FAQ
How do I calculate a percentage of an amount?
Multiply the amount by the percent and divide by 100: 15% of 2,000 = 300.
How do I find what percent one number is of another?
Divide the first by the second and multiply by 100: 30 of 120 = 25%.
How do I calculate a percentage increase?
Subtract old from new, divide by old, multiply by 100: 200 to 250 is +25%.
Is 20% off plus 10% off the same as 30% off?
No, it is 28% off, because the second discount applies to the reduced price.
How do I work out 15% quickly?
Take 10% by moving the decimal point, then add half of it: 15% of 300 = 30 + 15 = 45.
How do I find the original price before a discount?
Divide the sale price by (1 − discount): 315 after 30% off was 315 ÷ 0.7 = 450.