Percentage & Discount Calculator
Calculate percentages, discounted prices, and rates of change all in one place. Covers common cases like "what percent of B is A", "what's the discounted price of B", and "what's the percentage change from A to B". Everything runs in your browser — the numbers you enter are never sent anywhere.
The numbers you enter are processed entirely in your browser and never sent anywhere.
Enter numbers and press "Calculate".
How to use
- Choose a calculation type: basic percentage, discount, or percentage change.
- Pick a direction (where applicable) and enter the numbers.
- Press "Calculate" to see the result.
How it works
Basic percentage
Three directions are supported:
- What is a percentage of a base value: base value × percentage ÷ 100
- What percentage a value is of a base value: value ÷ base value × 100
- Find the base value when a value is a given percentage of it: value ÷ (percentage ÷ 100)
Discount
Three directions are supported:
- Original price + discount rate → final price: final price = original price × (1 − discount rate ÷ 100)
- Original price + final price → discount rate: discount rate = (original price − final price) ÷ original price × 100
- Final price + discount rate → original price: original price = final price ÷ (1 − discount rate ÷ 100)
Enter the discount rate as a value from 0 to 100 (below 100 when working out the original price from the final price). If the final price is higher than the original price (a price increase), the calculated discount rate will be negative — that's not an error, it represents the size of the increase.
Percentage change
Given a value before and after, this calculates the difference and the rate of change:
- Difference = value after − value before
- Rate of change (%) = difference ÷ value before × 100
An increase gives a positive value, a decrease gives a negative one. This can't be calculated if the "value before" is 0, since that would divide by zero.
About rounding
All results are rounded to 6 decimal places. This keeps calculations that don't divide evenly (e.g. what percentage 1 is of 3 → 33.333333%) from displaying an endless string of digits.
FAQ
Is the data I enter sent anywhere?
No. All calculations happen entirely inside your browser; nothing is transmitted externally.
What happens in the discount calculator if the final price is higher than the original price?
The calculated discount rate comes out negative. That's not an error — it represents a price increase rather than a discount.
Can I enter a discount rate above 100% or a negative one?
No. The discount rate must be between 0 and 100% (and below 100% when working out the original price from the final price — at exactly 100% the original price would be infinite and can't be calculated).
Why does the result sometimes have a long decimal?
When a percentage doesn't divide evenly (e.g. what percentage 1 is of 3), the result is rounded to 6 decimal places rather than showing an endless string of digits.
Can I calculate a percentage change starting from a negative number?
Yes. The only case that can't be calculated is when the starting value is exactly 0, since that would divide by zero.
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