Percentage Calculator
Percentages, differences and percentage change. Free, and runs entirely in your browser — nothing you enter is uploaded, stored or sent to a server.
About Percentage Calculator
Five calculations that are individually trivial and collectively easy to get backwards: X% of Y, X is what percent of Y, the change from X to Y, and adding or subtracting a percentage. Choosing the operation explicitly removes the usual source of error.
The one worth being careful with is percentage change, because it is not symmetric. A value falling from 100 to 80 is a 20% decrease; recovering from 80 to 100 is a 25% increase. Same two numbers, different base.
Where it helps
- Each operation is named, so there is no ambiguity about which way round it works.
- Handles increases and decreases with the correct base each time.
- Negative values and decimals are accepted.
- Instant, offline, and no spreadsheet required.
Limits
- Percentages do not compound the way intuition suggests: +10% then −10% lands below where you started.
- Percentage points and percent are different things — a rate moving from 5% to 7% is two points, not two percent.
- Results are floating point, so a long chain of calculations can drift in the last digits.
- It does no rounding for currency; do that at the end, according to your own rules.
Frequently asked questions
Why is a 20% fall not undone by a 20% rise?
The rise is calculated from the smaller number. From 100 down to 80 is −20%, but 80 back up to 100 is +25%.
How do I remove VAT or sales tax from a total?
Divide rather than subtracting a percentage: at 20%, divide by 1.2. Subtracting 20% from the gross gives the wrong answer.
What is the difference between percent and percentage points?
Moving from 5% to 7% is a rise of two percentage points, and also a 40% relative increase. Both are correct and they mean different things.
Can I chain several changes?
Yes, but feed each result into the next calculation. Percentages compound multiplicatively, so they cannot simply be added.
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