Percentage Decrease Calculator: Reduce a Number by X%

Enter a number and the percentage to take off it. You get the reduced value and the amount of the decrease.

Updated October 27, 2026

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Formula

new value = value × (1 - percent ÷ 100)

amount taken off = value × percent ÷ 100

Worked example

Decrease 200 by 15%: 200 × 15 ÷ 100 = 30, so the new value is 200 - 30 = 170.

Frequently asked questions

How do I decrease a number by a percentage?

Multiply the number by (1 - percent ÷ 100). To reduce 200 by 15%, calculate 200 × 0.85 = 170.

How do I find only the amount of the decrease?

Multiply the number by the percentage and divide by 100. For 200 and 15%, the decrease is 200 × 15 ÷ 100 = 30.

What happens at a 100% decrease?

The result is zero. For example, 55 decreased by 100% is 55 - 55 = 0. This calculator accepts 0 to 100%.

Is a 50% decrease undone by a 50% increase?

No. 80 decreased by 50% is 40, but 40 increased by 50% is only 60. To get back to 80 you need a 100% increase.

How we calculate

Percentage Decrease Calculator: Reduce a Number by X%

Formula

Worked example

Frequently asked questions

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