Free calculator

Percentage Decrease Calculator

Calculate percentage decrease and absolute reduction, or find the original value before a discount or decrease.

How to use this tool

Compare a smaller new value with its non-zero original value, or reverse a decrease to recover the original value.

Transparent method

Formula and method

Decrease % = |((new − original) ÷ |original|) × 100|. Reverse: original = final ÷ (1 − decrease ÷ 100).

Worked examples

Standard decrease: 120 to 100 is approximately a 16.666667% decrease and an absolute decrease of 20.
Discount example: 100 to 75 is a 25% decrease and an absolute decrease of 25.
Reverse discount: a final value of 75 after a 25% decrease corresponds to an original value of 100.
Asymmetry: 100 to 150 is a 50% increase, but 150 to 100 is approximately a 33.333333% decrease.

Assumptions and limits

The original value cannot be zero.
The new value must be less than or equal to the original value.
Reverse mode accepts a decrease from 0% up to, but not including, 100%.
Negative values follow the shared formula and direction is determined by the signed difference.

What is percentage decrease?

Percentage decrease measures a reduction relative to the magnitude of the original value. Absolute decrease measures only the numeric difference between the original and new values.

Percentage decrease formula

Subtract the new value from the original value, divide by the absolute original value and multiply by 100. The shared engine retains a negative signed change, while this focused page displays the decrease magnitude as a positive percentage.

For 120 to 100, the decrease is 20 ÷ 120 × 100, or approximately 16.666667%.

How to calculate a discount

Use the listed price as the original value and the sale price as the new value. A price falling from 100 to 75 has a 25% decrease, so the discount is 25% of the original price.

Find an original price before a discount

Divide the final price by 1 minus the decrease written as a decimal. A sale price of 75 after a 25% discount gives 75 ÷ 0.75 = 100.

The reverse mode supports decreases from 0% up to, but not including, 100%. At 100% the final value loses the information needed to recover a unique original value.

Why equal increases and decreases do not cancel out

Increasing 100 by 50% gives 150. Decreasing 150 by 50% gives 75, not 100, because the second percentage uses 150 as its starting value.

Returning from 150 to 100 requires a decrease of approximately 33.333333%, not 50%.

Percentage decrease in Excel and Google Sheets

If A1 is the original and B1 is the new value, use =(A1-B1)/ABS(A1), then apply percentage formatting. To recover an original price from final price A1 and discount rate B1, use =A1/(1-B1).

Common mistakes include dividing by the final value, confusing absolute reduction with percentage decrease, using a zero original value and attempting to reverse a 100% discount.

Frequently asked questions

How do I calculate percentage decrease?

Subtract the new value from the original value, divide by the absolute original value and multiply by 100.

How do I calculate a discount percentage?

Treat the listed price as the original and the sale price as the new value. The percentage decrease is the discount percentage relative to the listed price.

How do I find the original price before a discount?

Divide the sale price by 1 minus the discount as a decimal. For example, 75 ÷ 0.75 gives an original price of 100.

Why do equal percentage increases and decreases not cancel out?

They use different starting values. A 50% increase from 100 reaches 150, while a 50% decrease from 150 reaches 75.

Can percentage decrease exceed 100%?

The general change formula can produce changes below -100% when values cross zero, but the focused reverse discount mode is limited to decreases below 100%.

What happens if the original value is zero?

Percentage decrease from zero has no finite conventional result because the formula divides by the original value. CorelyUp reports an error instead of Infinity.