How to Calculate Percentage Change: A Step-by-Step Guide

The four steps

1. Identify the old value and the new value. The old value is where you started; the new value is where you ended up. Getting these backwards flips the sign of your answer.
2. Subtract the old value from the new value. New − Old. This is the raw amount of change, before it's turned into a percentage.
3. Divide by the absolute value of the old value. (New − Old) ÷ |Old|. Taking the absolute value keeps this working correctly even if the old value happens to be negative.
4. Multiply by 100. That turns the decimal into a percentage. A positive result is an increase; a negative result is a decrease — the sign tells you the direction automatically.

Example 1: A price increase

A subscription price goes from $8 to $10 per month.

1. Old = 8, New = 10
2. 10 − 8 = 2
3. 2 ÷ |8| = 0.25
4. 0.25 × 100 = 25% increase

Example 2: A decrease

Website traffic drops from 4,200 visits to 3,150 visits in a month.

1. Old = 4,200, New = 3,150
2. 3,150 − 4,200 = −1,050
3. −1,050 ÷ |4,200| = −0.25
4. −0.25 × 100 = −25%, a 25% decrease

Example 3: A negative starting value

A business's cash position moves from −$25,000 to $25,000.

1. Old = −25,000, New = 25,000
2. 25,000 − (−25,000) = 50,000
3. 50,000 ÷ |−25,000| = 50,000 ÷ 25,000 = 2
4. 2 × 100 = 200% change

Without the absolute value in step 3, a negative old value would flip the sign of the whole result and give a misleading answer. This is the one step people skip most often when calculating by hand.

Check your work

Once you've calculated a percentage change by hand, it's worth double-checking with the calculator — especially for negative values or numbers with several decimal places, where a small arithmetic slip is easy to miss.

Verify your answer with the Percentage Change Calculator →

If your number only ever goes up, the Percentage Increase Calculator is a more direct fit for that case. And if you're not sure "change" is even the right concept for what you're comparing, see Percentage Change vs. Percentage Difference vs. Percentage Points.

Sources

• Percentage Change — Math Is Fun
• Percentage Change Calculator — CalculatorSoup

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