How to Write a Percentage Change Formula in Excel

Bottom Line: Understanding the percentage change formula can help you make better decisions, especially when analyzing data for conversions, sales, or performance.

Skill Level: Beginner

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Download the Excel File

You can access the simple Excel file I use in the video here.

Percentage Change

Calculating percentage change in Excel is essential for anyone who works with data. Whether you're analyzing website conversions, sales, or even sports statistics, knowing the correct formula can help you avoid costly mistakes. In this post, we will walk through the steps to accurately calculate percentage change

What is the percentage change formula? The formula to calculate percentage change is:

Percentage Change = (Value 2 – Value 1) / Value 1

This formula compares one value to another value and expresses the difference as a percentage.

Example Scenario: Website Conversion Rates

Let’s start with an example. Suppose we have two webpages with different conversion rates:

• Page A has a conversion rate of 3%.
• Page B has a conversion rate of 5%.

At first glance, it might seem like the difference between these two pages is only 2%. However, when we apply the percentage change formula, we see the real difference is 66.7%, not 2%.

Formula: Percentage Change = (5% – 3%) / 3% = 2 / 3 = 66.7%

This shows that Page B is performing 66.7% better than Page A.

Conversion Rates with Different Data Sets

The reason we calculate percentage change instead of just comparing the number of conversions is because the number of visitors to each page differs. Let’s say:

• Page A has 6,000 visitors, yielding 180 buyers.
• Page B has only 100 visitors, yielding 5 buyers.

In this case, you cannot directly compare 180 to 5, but you can still compare the conversion rates (3% vs. 5%) to calculate percentage change, which remains 66.7%.

Calculating Percentage Change in Excel

Let’s now see how you can apply this in Excel. The way I like to remember the formula is simply

1. New minus Old over Old:
   In Excel, your formula would be something like this:
   
   =(D5 – C5) / C5
   where D5 is the new value (5%) and C5 is the old value (3%).

Another way to calclulate percentage change is:

2. New over Old minus 1:
   This simplified version of the formula would look like this in Excel:
   
   =D5 / C5 – 1

Both formulas give the same result, but the second requires fewer keystrokes and might be easier to use in spreadsheets.

I tend to use the first way when I'm doing the math in my head, and the second way when I'm calculating using a calculator or in Excel.

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Order of Numbers Matters

What happens if we reverse the values? If Page A has a conversion rate of 5% and Page B has a rate of 3%, the percentage change becomes -40%, indicating that Page B is underperforming by 40%.

A Wide Range of Uses

You can also use percentage change formulas in other scenarios, like:

• Sales Discounts: Compare the sale price to the original price.
• Sports Statistics: Compare performance rates between two players.
• Survey Results: Measure improvement between response rates.
• Lost Shipments: Find out if your modified procedures are preventing loss.
• Opt-In Rates: Does page setup affect how many signups you get?

Final Thoughts

Whether you prefer the formula New – Old / Old or New / Old – 1, mastering percentage change will help you make better data-driven decisions. Don't forget to teach this formula to your team—it could save you a lot of money!

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