How to use the Percentage Calculator
Last verified 2026-08-08 · about 5 minutes to read
The short version
- 1.Pick the question. Six shapes cover almost every percentage problem. Choosing the right one is most of the work.
- 2.Enter A and B. The labels above the answer tell you which number the calculator read as which.
- 3.Copy the working, not just the answer. The substituted formula is shown so you can paste it into an email or a homework answer.
Why this is worth getting right
Every answer comes with the substituted formula, not just a number. That is the difference between a calculator and an answer you can defend in a meeting or a marked assignment. Percentage change additionally reports percentage points alongside percent, because conflating the two is the most common quantitative error in business reporting.
Method 1 — use the Percentage Calculator on this site
The fastest route. It runs entirely in your browser, so nothing is uploaded and there is no queue to wait in. No account is needed and there is no daily limit.
- Pick the question. Six shapes cover almost every percentage problem. Choosing the right one is most of the work.
- Enter A and B. The labels above the answer tell you which number the calculator read as which.
- Copy the working, not just the answer. The substituted formula is shown so you can paste it into an email or a homework answer.
Open the Percentage Calculator →
Method 2 — do it without this site
Worth knowing, because a tool you cannot replace is a dependency rather than a convenience. Most tasks in the calculators division have a command-line or built-in equivalent; it is usually more setup and less convenient, but it works offline and it is scriptable, which matters once you are doing something a hundred times instead of once.
What this tool will not do
Every tool has an edge. These are ours for percentage calculator, stated up front so you find out here rather than halfway through a deadline:
- Percentage change from zero is undefined and is reported as an error rather than as infinity.
- Results are rounded to four decimal places for display; the underlying arithmetic is full double precision.
- This is not compound interest. Repeated percentage changes need the compound interest calculator.
Questions people ask
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 200 is 15 ÷ 100 × 200 = 30. Select "What is A% of B?" and the calculator shows that substitution with your own figures.
What is the difference between percentage change and percentage points?
If a rate moves from 5% to 6%, that is a rise of one percentage point and a rise of twenty percent. Both are correct and they mean very different things. This calculator reports both whenever you compute a change, because conflating them is the single most common percentage error in reporting.
How do I calculate percentage increase?
Subtract the old value from the new one, divide by the old value, and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%. The order matters: dividing by the new value instead gives 20%, which is a different question.
Why is a 50% rise followed by a 50% fall not back where it started?
Because each percentage applies to a different base. 100 rises by 50% to 150, then falls by 50% of 150, which is 75, landing at 75. Reversing a 50% increase requires a 33.3% decrease. Percentages do not commute.
How do I find the original price before a discount?
Use "A is B% of what number?". If an item costs 80 after a 20% discount, it is 80% of the original, so 80 ÷ 80 × 100 = 100. Do not add 20% to 80 — that gives 96, which is a common and expensive mistake.