How to use the Percentage Calculator
- Pick the box (① to ④) that matches what you want to find.
- Type a number into each of the two fields and the result appears instantly. Enter plain numbers without commas.
- The formula and the numbers it used appear below the result, so you can copy them straight into homework or a report.
- In box ④, use the Increase and Decrease buttons to switch between the raised and the reduced amount.
Percentage formulas at a glance
| What you want | Formula | Example |
|---|---|---|
| B% of A | A × B ÷ 100 | 15% of 80,000 = 12,000 |
| A is what % of B | A ÷ B × 100 | 45 is 75% of 60 |
| Percent change | (B − A) ÷ A × 100 | 200 → 250: +25% |
| Increase A by B% | A × (1 + B ÷ 100) | $300 raised 10% = $330 |
| Decrease A by B% | A × (1 − B ÷ 100) | $300 cut 10% = $270 |
"Percent" means "per hundred," so every percentage calculation involves dividing by 100 or multiplying by 100 at some point.
Percent change vs. percentage points
When a rate itself moves, the difference between the two rates is measured in percentage points. For example, if an interest rate goes from 3% to 4%, it rose by "1 percentage point," but the percent change is (4 − 3) ÷ 3 × 100 = about a 33.3% increase.
A news report saying "approval rose 4 percentage points, from 40% to 44%" and one saying "approval rose 10%" are describing the same change in two different ways. When you write a report, make it clear which one you mean.
If something goes up 10% and then down 10%, is it back where it started?
No. If $100 goes up 10%, it becomes $110. Take 10% off that and you get 110 × 0.9 = $99, because the second percentage is applied to a bigger starting value.
To get back to the original value, you would need a drop of 10 ÷ 110 × 100 = about 9.09%. People often get this wrong when comparing values that rise and fall in a row, like stock prices or sales, so check it yourself in box ③. If you're stacking several discounts, the stacked-discount option in the discount calculator is handy.
Everyday percentage examples
- Test scores: Got 42 out of 50 questions right? Enter 42 and 50 in box ② to get a score of 84%.
- Pay raises: A $60,000 salary with a 4% raise: enter 60000 and 4 in box ④ to get $62,400.
- Sales growth: $120,000 last year and $150,000 this year shows up in box ③ as +25% growth.
- Tips and fees: An 18% tip on a $68 bill comes out to $12.24 in box ①. A 2.9% card fee on $680 comes to $19.72.
- Sale prices: A $45 item marked 30% off: enter 45 and 30 in box ④ and choose Decrease to get $31.50.
Quick mental math tricks
- 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).
- Swap trick: A% of B equals B% of A, so 8% of 50 is the same as 50% of 8, which is 4.
These are good for quick estimates. Use the calculator when you need an exact figure.