Reckoner.
What is % of ?
Result
0
About Reckoner
Reckoner works out the four most common percentage questions, updating the answer live as you type. Nothing you enter is uploaded or sent to a server.
Features
- Find what X% of a number is
- Find what percentage one number is of another
- Calculate percentage increase or decrease between two numbers
- Add or subtract a percentage from a number
- Live results as you type — no button to press
- Runs entirely in your browser — nothing is uploaded
How to use it
- Pick the question that matches what you're trying to find.
- Fill in the numbers in the sentence — the answer updates as you type.
- For "plus/minus," choose whether you're adding or subtracting the percentage.
Frequently asked questions
What's the difference between "% of" and "is what %"?
"What is X% of Y" finds a portion of a number — like 20% of 150 is 30. "X is what % of Y" works backward from a known portion to find the percentage it represents — like 30 is 20% of 150.
How is percentage change calculated?
It's the difference between the two numbers, divided by the starting number, expressed as a percentage. A positive result means an increase; a negative result means a decrease.
Can I use negative numbers?
Yes, all four calculators accept negative numbers and will return a mathematically correct result.
Is my data sent anywhere?
No. All calculations happen locally in your browser using plain JavaScript — nothing is uploaded to a server.