Percentage Calculator
Four calculations, kept separate.
- Nothing is sent to a server
- Instant results
- Free, no sign-up
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Questions
Why doesn't a 50% fall followed by a 50% rise get me back to where I started?
Because the rise applies to a smaller number. $100 falling 50% is $50; rising 50% from there is $75, not $100. To recover from a 50% fall you need a 100% gain. The pattern gets steeper: a 25% fall needs a 33% gain, an 80% fall needs 400%. This is the most common percentage error there is.
What is the difference between a percent and a percentage point?
If an interest rate moves from 4% to 5%, that is a rise of one percentage point but a 25% increase. Both statements are correct and they mean very different things, which is exactly why the distinction gets exploited in advertising and political claims. When a figure sounds surprising, check which one is meant.
Do stacked discounts add up?
No. '30% off, then an extra 20% off' is not 50% off — it is 0.7 × 0.8 = 0.56, so 44% off. Sequential discounts always come to less than their sum, because each one applies to a smaller amount than the last. The same logic applies to sequential price increases.
What is the difference between margin and markup?
Markup is calculated on cost, margin on selling price. A product costing $100 sold at a 25% markup is $125; sold at a 25% margin it is $133.33. Confusing the two is a common and expensive pricing error for small businesses, because it systematically underprices.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100 — 30 out of 200 is 30 ÷ 200 × 100 = 15%. Use the 'X is what % of Y' tab above. The order matters and getting it backwards is easy: 200 out of 30 would be 667%.
About percentage calculator
Four different questions
“Percentage” covers several distinct calculations that people routinely mix up, which is why this tool separates them rather than offering one box.
- X% of Y — a share of a known amount. 15% of $200 is $30.
- X is what % of Y — expressing one number as a share of another. 30 out of 200 is 15%.
- Percentage change — how much something moved. From 200 to 250 is a 25% increase.
- Add or subtract a percentage — applying a discount or a markup. 200 less 10% is 180.
A rise and a fall of the same percentage do not cancel
This is the most common percentage error there is. A stock that falls 50% and then rises 50% is not back where it started — it is down 25%, because the 50% rise applies to the smaller number. To recover from a 50% fall you need a 100% gain.
| Fall | Gain needed to recover |
|---|---|
| 10% | 11.1% |
| 25% | 33.3% |
| 50% | 100% |
| 80% | 400% |
Percent versus percentage point
If an interest rate moves from 4% to 5%, that is a rise of one percentage pointbut a 25% increase. Both are correct and they mean very different things, which is exactly why the distinction gets exploited in advertising and political claims. When a figure sounds surprising, check which one is meant.
Discounts do not stack the way they look
“30% off, then an extra 20% off” is not 50% off. It is 0.7 × 0.8 = 0.56, so 44% off. Sequential discounts always come to less than their sum, because each applies to a smaller amount than the last.
The same applies to markups: a 25% margin and a 25% markup are different numbers. A product costing $100 sold at a 25% markup is $125; sold at a 25% margin it is $133.33.
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