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Percentage Increase & Decrease Calculator

Compare an old and new value to get the percentage increase or decrease — for prices, salaries, traffic, weight or anything else.

Quick answer

Percentage change = (new − old) ÷ old × 100. Going from 80 to 100 is a 25% increase; from 100 back to 80 is a 20% decrease, because the starting value changed.

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  • Everyday
  • Updated October 2026

Percentage increase

25%

Change in value
+20
Percentage difference (symmetric)Compares the gap to the average of both values.
22.22%
Show the working
  1. (100 − 80) ÷ |80| × 100 = 25%

About the Percentage Increase & Decrease calculator

Percentage change measures how much something moved relative to where it started. It is the standard way to report price rises, salary increases, website traffic and sales growth.

Percentage difference is different: it compares two values with no “before” or “after”, using their average as the baseline. Both are shown so you can use whichever fits.

How to use it

  1. Enter the original (starting) value.
  2. Enter the new value.
  3. The result is labelled as an increase or a decrease automatically.

The formula

Change % = (New − Original) ÷ |Original| × 100

  • Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100.

Worked example

A rent increase

  1. Rent goes from $1,200 to $1,350.
  2. $1,350 − $1,200 = $150.
  3. $150 ÷ $1,200 = 0.125 → a 12.5% increase.

Frequently asked questions

Why is a 50% drop followed by a 50% rise not back to the start?

Each percentage is applied to a different base. $100 down 50% is $50; $50 up 50% is only $75. To recover a 50% drop you need a 100% rise.

Can percentage change be more than 100%?

Yes, for increases. Going from 20 to 70 is a 250% increase. A decrease can never exceed 100%, unless the value turns negative.

What if the original value is zero?

Percentage change is undefined because you cannot divide by zero. Report the absolute change instead.

Results are estimates for planning — check critical figures with a professional or the official source.

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