How this calculation works
Use a positive percentage for an increase and a negative percentage for a decrease. Divide by the growth factor instead of subtracting that percentage from the final amount.
Original = final ÷ (1 + percentage change ÷ 100)A worked example
A final amount of 120 after a 20% increase came from 100.
Good to know
Uses the stated formula and assumptions. Displayed decimal values are rounded; use consistent units for all inputs.
Undo the multiplier, not the percentage label
Suppose a sale price of ₹800 follows a 20% discount. The sale price is 80% of the original, so divide ₹800 by 0.8 to recover ₹1,000. Adding 20% to ₹800 gives ₹960, which does not undo the discount.
For an increase, the same logic applies. A total of ₹1,180 after an 18% increase comes from ₹1,000 because 1,180 ÷ 1.18 = 1,000. The operation is division by the original growth factor.
A total loss cannot be uniquely reversed
After a 100% decrease, every possible starting amount becomes zero. The final value no longer contains enough information to identify the original amount. This is why the tool does not accept −100% as a reversible change.
Successive changes must be combined by multiplication before reversal. Two 10% increases produce a factor of 1.1 × 1.1 = 1.21, so their total increase is 21%, not 20%.
A few questions, answered
How do I reverse a discount?
Enter the discounted amount and a negative change, such as −20 for a 20% discount.
How do I reverse an increase?
Enter the final amount and a positive percentage change.