How to Calculate Percentage Decrease

Percentage decrease measures how much a value has fallen compared with where it started. It is the same idea as percentage increase with the subtraction turned around.

The formula

Percentage decrease = (original value − new value) ÷ original value × 100

Example: a price drop

A jacket falls from 120 to 90.

1. Drop: 120 − 90 = 30
2. Divide by the original: 30 ÷ 120 = 0.25
3. Multiply by 100: 25%

Subtracting a percentage from a number

To take a percentage off a number, multiply by 1 minus the percentage as a decimal.

New value = original × (1 − percentage ÷ 100)

Reduce 120 by 25%: 120 × 0.75 = 90. The amount removed is 30.

Reversing a decrease

If something costs 90 after a 25% reduction, the original was 90 ÷ 0.75 = 120. Adding 25% to 90 would give 112.50, which is wrong, because the 25% was taken from the larger original number.

Why the direction matters

A drop from 120 to 90 is 25%, but a rise from 90 back to 120 is a 33.3% increase, because 30 ÷ 90 = 0.333. The size of the change is the same, but the starting point differs, so the percentages differ.

Common mistakes

• Dividing by the new value. Always divide by the original.
• Adding the percentage back to reverse a cut instead of dividing by the multiplier.
• Stacking decreases. Two successive 10% decreases make 19%, not 20%, because 0.9 × 0.9 = 0.81.

The percentage decrease calculator works both ways and switches to an increase automatically if the new number is higher.

Try it yourself

1. A value falls from 500 to 425. What is the percentage decrease?
2. Reduce 64 by 37.5%.
3. A price is 48 after a 20% cut. What was the original price?

Answers: (1) 15%; (2) 40; (3) 60 (48 ÷ 0.8).