Percentage Calculator
Solve eight kinds of percentage problem: what percent one number is of another, a percentage of a number, percentage change, percentage difference, percent ↔ decimal, and percent ↔ fraction. Shows the result, a plain-English summary and the formula used.
Input
Output
Guides
One calculator for the eight percentage questions people actually ask. Pick the calculation, type the numbers, and get the answer, a plain-English sentence you can paste into an email, and the formula used to get there.
The eight calculations
| Calculation | Example | Answer |
|---|---|---|
| Percentage of total | 16 out of 20 is what percent? | 80% |
| Percentage of a number | What is 10% of 500? | 50 |
| Percentage change | From 20 to 100 | 400% |
| Percentage difference | Between 500 and 450 | 10.53% |
| Percent to decimal | 15% | 0.15 |
| Decimal to percent | 0.025 | 2.5% |
| Percent to fraction | 20% | 1/5 |
| Fraction to percent | 12/15 | 80% |
How to use it
Choose a calculation from the Calculation dropdown — the input fields change to match. Results update as you type. Every answer is rounded to two decimal places and trailing zeros are trimmed, so you get 80%, not 80.00%.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100: 16 ÷ 20 × 100 = 80%. This is the Percentage of total mode, and it is the calculation behind test scores, conversion rates and "what portion of the budget did we spend".
What is the difference between percentage change and percentage difference?
They are not the same thing, and mixing them up is a common source of wrong numbers.
- Percentage change is directional. It measures movement from a starting value to a new one, dividing by the original:
(new − old) ÷ old × 100. Going from 20 to 100 is a 400% increase; going from 100 back to 20 is an 80% decrease. The two are not symmetric. - Percentage difference is symmetric. It compares two values with no notion of "before", dividing by their average:
|a − b| ÷ ((a + b) ÷ 2) × 100. The difference between 500 and 450 is 10.53%, whichever order you put them in.
Use change for anything over time (revenue, price, weight). Use difference when comparing two independent measurements.
How do I convert a percentage to a fraction?
Divide by 100 and simplify: 20% becomes 20/100, which reduces to 1/5. This tool does that with exact integer arithmetic rather than floating-point, so 33.3% gives you 333/1000 and not an approximation. Results greater than 1 are shown as mixed numbers — 150% becomes 1 1/2.
Can I enter mixed numbers?
Yes. The Fraction to percent mode accepts a simple fraction (3/4), a mixed number (2 2/3) or a plain decimal (0.75).
Why is my percentage increase over 100%?
Because the new value is more than double the old one. Growing from 20 to 100 means adding 80 to a base of 20 — four times the base — so the increase is 400%. A percentage increase has no upper limit; a percentage decrease can never exceed 100%, because that would take the value below zero.
Privacy
Everything is calculated in your browser. No numbers are sent to a server.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/percentage-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"type": "type-1",
"type1A": "16",
"type1B": "20"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `percentage-calculator` tool (Percentage Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.