Math calculator
Reverse Percentage Calculator
Find the original amount when you know a percentage and its resulting value.
How this calculation works
Original amount = known amount ÷ (percentage ÷ 100) Use the calculator above to enter your values. Inputs are checked before a result is shown, and calculations run locally in your browser.
30 is 20% of 150: 30 ÷ 0.20 = 150.
45 is 15% of 300: 45 ÷ 0.15 = 300.
12 is 4% of 300: 12 ÷ 0.04 = 300.
Frequently asked questions
How does the reverse percentage calculator work?
Original amount = known amount ÷ (percentage ÷ 100)
What is an example?
If 30 is 20% of the original amount, the original is 30 ÷ 0.20 = 150.
Can I enter decimal values?
Yes. Enter decimal values where appropriate. The calculator checks required inputs and displays a readable result.
Are results rounded?
Results are formatted for readability. Check the displayed formula and units when using the result.
Keep calculating