Percentage Decrease Calculator

Measure a reduction relative to an original value.

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Formula / Calculation Method

Decrease % = (old − new) / old × 100.

A decrease from 100 to 80 is 20%.

The original value must be positive. A negative result indicates an increase.

Measure a reduction relative to an original value.

Enter the original positive value and the new nonnegative value after the change.

Select Calculate after entering your values. Text tools update as you type. Reset restores the starting fields.

A positive decrease means the value fell; a negative decrease means it grew. A drop from 100 to 80 is 20%, while the rise from 80 back to 100 is 25%.

Can the decrease be negative?

Yes. That indicates an increase relative to the original value.

What assumptions does this tool use?

The original value must be positive. A negative result indicates an increase.

Find a percentage of a number.

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