Percentage Increase / Decrease Calculator

Increase or decrease a starting value by a percentage, or work out the percent change between two numbers. The calculator shows both the amount of change and the final value.

Choose a mode and enter your numbers.

The percentage change formula

To apply a percentage to a value, convert the percent to a decimal and multiply. To increase by p%, multiply by (1 + p ÷ 100); to decrease, multiply by (1 − p ÷ 100). To find the percent change between two numbers, compare the difference to the original.

change% = (new − old) ÷ |old| × 100

A positive result is an increase, a negative result is a decrease. Using the absolute value of the old number keeps the sign meaningful even when the starting value is negative.

Worked example

Increase 200 by 15%:

Amount of change: 200 × 0.15 = 30.
New value: 200 + 30 = 230.
Going the other way: from 200 to 230 is (230 − 200) ÷ 200 × 100 = 15% — the math is consistent.

Increase vs decrease aren't symmetric

A common trap: a 20% rise followed by a 20% fall does not return you to the start. 100 → +20% → 120 → −20% → 96, because the second percentage is taken from the larger number. That's why the percent change between two values is calculated from the original value, not the new one. This calculator handles all three directions so you can move from value-and-percent to a result, or from two values back to a percent.

Tip: comparing an old and new figure directly? The percentage change calculator focuses on that, and the discount calculator handles sale prices and stacked discounts.

Frequently asked questions

How do I increase a number by a percentage?

Multiply the number by (1 + percent ÷ 100). For example, to add 15% to 200, multiply 200 by 1.15 to get 230. The amount of the increase is 200 × 0.15 = 30.

How do I decrease a number by a percentage?

Multiply by (1 − percent ÷ 100). To take 15% off 200, multiply 200 by 0.85 to get 170. The amount removed is 200 × 0.15 = 30.

Why doesn't a 20% rise then 20% fall undo itself?

Because each percentage applies to a different base. 100 + 20% = 120, but 20% of 120 is 24, not 20, so 120 − 24 = 96. The fall is taken from the larger number, so you end up below where you started.

How is percent change between two numbers found?

Subtract the old value from the new, divide by the absolute value of the old, and multiply by 100. A positive answer is an increase; a negative one is a decrease.

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Mustafa Bilgic · Editor, Calcool
Applies the standard percentage-change formula; increase and decrease are not symmetric because each percent uses a different base. Everything runs in your browser — nothing you enter is uploaded, logged or stored.

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