How to use the Percentage Calculator
- Find the question that matches what you need, such as What is __% of __?
- Type your two numbers. The answer updates as you type.
- Click Copy to use the result, and read the formula underneath to see how it was worked out.
Percentage formulas
| X% of Y | X ÷ 100 × Y. 15% of 80 = 12. |
|---|---|
| X is what % of Y | X ÷ Y × 100. 12 is 15% of 80. |
| % change from A to B | (B − A) ÷ |A| × 100. From 80 to 100 is a 25% increase. |
| Increase X by Y% | X × (1 + Y ÷ 100). 80 + 25% = 100. |
| Decrease X by Y% | X × (1 − Y ÷ 100). 100 − 20% = 80. |
| % difference | |A − B| ÷ ((A + B) ÷ 2) × 100, used when neither value is the "original". |
Percentage change vs percentage points
If an interest rate rises from 2% to 3%, it went up by 1 percentage point, but by 50 percent. News reports mix these up all the time. Use percentage points for the difference between two percentages, and percent change for how much something grew relative to where it started.
Why +20% then −20% doesn't get you back
A 100 baht item raised by 20% costs 120. A 20% discount on 120 takes off 24, leaving 96. The second percentage applies to a bigger number. To undo a 20% increase you need a 16.67% decrease.
Frequently asked questions
How do I work out a discount?
Use <b>Decrease __ by __%</b>: enter the price and the discount. For 30% off 1,200, the sale price is 840.
How do I add VAT or tax?
Use <b>Increase __ by __%</b> with the tax rate, e.g. 7% VAT on 1,000 gives 1,070.
How do I find the original price before a discount?
Use <b>__ is __% of what?</b>: if 840 is the price after 30% off, enter 840 and 70 (100 − 30). The original was 1,200.
Can I use decimals and negative numbers?
Yes. Commas as thousands separators are ignored, so 1,250.5 works.