How to Find the Original Value Before a Percentage Change
Reverse a percentage without the simple-subtraction trap.
What it does and when to use it
When the final value and increase are known, subtracting the same percentage does not usually reverse the change. Divide by the growth factor.
What information to enter
Enter the value after the increase and the percentage increase.
How to understand the result
The result is the base value on which the percentage was applied.
Formula at a glance
Original value = final value ÷ (1 + percentage ÷ 100)
Short example
A price of $120 after a 20% increase started at $100 because 120÷1.2=100.
Common mistakes
- Subtracting 20% from 120 and getting 96, which uses a different base.
- Entering -100%, which creates a zero factor and cannot be reversed.
Frequently Asked Questions
How do I reverse a discount?
Divide the final price by one minus the discount rate.
Why do equal increase and decrease rates not cancel?
The second rate is applied to a different base.