Percentage Calculator: Percent of a Number, Percent Change and Finding the Original Value
The common percentage problems, solved with the steps.
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How this calculator works
Choose the type of problem.
Enter the numbers as the labels describe.
The calculator gives the answer with the working and a check.
Formulas used
- p\%\text{ of }X = \frac{p}{100}X
- \frac{A}{B}\times100
- \frac{\text{new} - \text{old}}{\text{old}}\times100
- \text{original} = \frac{\text{value after}}{1 + p/100}
Worked example
With the default numbers in the calculator above:
- The percent of the number: 36.00
- The number increased by that percent: 276.00
- The number decreased by that percent: 204.00
Change the numbers in the calculator to see the full working, every step, for your own case.
A second worked example
A different case, with these numbers: What do you want? Percent change from old to new; The number (or the old value, or the number B, or the value after the change) 80; The number A (the "is" case), or the new value (the change case) 100.
- Percent change from the old value to the new value: 25.00 % (an increase)
- The change in the value: 20.00
Common questions
How do I find the original price before a percentage increase?
Divide the new price by 1 plus the percent as a decimal. A price of 115 after a 15 percent rise was 100.
How do I work out percent change?
Subtract the old value from the new, divide by the old and multiply by 100.
Why does a 25 percent rise then a 25 percent fall not return to the start?
The fall is 25 percent of the larger number, so it takes off more than the rise added.
Related calculators
Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: Any school mathematics text (percentages).
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