Percentage Calculator
Find X% of Y, calculate increases, discounts, and percentage changes.
Three building blocks: 10%, 1%, and 5%
You can calculate almost any percentage in your head by combining a few simple building blocks:
- 10%: Divide by 10, or move the decimal point one place to the left. 10% of 350 = 35; 10% of 87 = 8.7.
- 1%: Move the decimal point two places to the left. 1% of 350 = 3.5; 1% of 1,240 = 12.4.
- 5%: Take half of 10%. 5% of 350 = 35 ÷ 2 = 17.5.
- 50%, 25%, and 20%: Take half, one-quarter, and one-fifth. 25% of 360 = 90; 20% of 45 = 9.
Use these building blocks to find other percentages by adding or subtracting:
| Calculation | How to work it out | Result |
|---|---|---|
| 15% of 80 | 10% (8) + 5% (4) | 12 |
| 18% of 250 | 10% (25) + 5% (12.5) + 3 × 1% (7.5) | 45 |
| 9% of 300 | 10% (30) − 1% (3) | 27 |
| 35% of 60 | 25% (15) + 10% (6) | 21 |
| 12.5% of 64 | one-eighth of 64 | 8 |
The swap trick
A percentage is multiplication, and changing the order of the factors doesn’t change the product. That means x% of y equals y% of x. Use whichever side is easier to calculate:
- 8% of 25 = 25% of 8 = 2.
- 16% of 50 = 50% of 16 = 8.
- 4% of 75 = 75% of 4 = 3.
- 36% of 25 = 25% of 36 = 9.
This works because 8% of 25 is 8 × 25 ÷ 100, which is the same as 25 × 8 ÷ 100.
Think in terms of multipliers
For purchases, salaries, and tests, the quickest approach is to turn an increase or discount into a factor:
- 12% increase → multiply by 1.12.
- 30% discount → multiply by 0.70.
- 5% increase → multiply by 1.05.
Find the original amount: If a price is $150.00 after a 25% increase, the original price was $150.00 ÷ 1.25 = $120.00 before the increase—not $112.50, which is what you get by subtracting 25% of 150. This is a common mistake on tests.
Find the percentage: Divide the part by the whole. 45 is what percent of 180? 45 ÷ 180 = 0.25 = 25%. You can also set it up as a proportion with the Rule of three (proportion) calculator to get the same result.
Successive increases and discounts
Successive percentage changes aren’t added; they’re multiplied because each one applies to the amount after the previous change.
| Scenario | Calculation | Overall change |
|---|---|---|
| +10%, then +20% | 1.10 × 1.20 = 1.32 | +32% (not 30%) |
| +20%, then −20% | 1.20 × 0.80 = 0.96 | −4% (not zero) |
| 30% discount, then another 10% | 0.70 × 0.90 = 0.63 | −37% (not 40%) |
| +25%, then −20% | 1.25 × 0.80 = 1.00 | 0% (back to the original price) |
The last example is a classic test question: a product that goes up 25% and then drops 20% returns to its original price. Try it with $100.00: it rises to $125.00, then a 20% discount ($25.00) brings it back to $100.00.
Worked example: A $2,400.00 salary gets a 5% raise, then another 4% raise a few months later. What’s the final salary and total increase? First raise: 2,400 × 1.05 = $2,520.00. Second raise: 2,520 × 1.04 = $2,620.80. The combined factor is 1.05 × 1.04 = 1.092, or a total increase of 9.2%, not 9%. In your head: 5% of 2,400 is 120; 4% of 2,520 is 100.80; add them for an increase of 220.80.
Percentages and percentage points
If a credit card’s interest rate rises from 10% to 12% per month, it goes up by 2 percentage points, but that’s a 20% increase from the previous rate (2 ÷ 10). News articles and test questions often highlight this difference, so read carefully to see which one is being asked for.
To check larger calculations, such as a discount on an installment purchase or a salary increase, use the Percentage Calculator to see the answer and the steps. For problems involving three or more quantities, see our guide to the compound rule of three.
Updated October 2026.
Frequently asked questions
How do you calculate 15% in your head?
Find 10% by moving the decimal point one place to the left, then add half that amount for 5%. For example, 15% of 80 is 8 plus 4, which equals 12.
Are two 10% discounts the same as 20% off?
No. Two successive 10% discounts mean multiplying by 0.9 twice, which gives 0.81—a total discount of 19%.
How do you find the original price after an increase?
Divide by the increase factor. If $150.00 includes a 25% increase, the original price was 150 divided by 1.25, or $120.00.