When To Use It
A bedrock of marketing is the calculation of percent change. (Real analysts call it percent delta … just so you know.) We use these to show month-over-month (MoM) and year-over-year (YoY) changes in data, and they should be in every reporting dashboard you build. Without exception.
What is amazing to me is that Excel doesn’t have this critical function built in. So if you need to know the binomial distribution for a Bernoulli experiment, no prob, Bob! Excel’s got your back. But the percent delta between two numbers? Don’t get crazy!
How To Do It In Excel
So the first thing to remember is forget what you learned in middle school algebra. I find the easiest way to remember how to calculate percent delta is this:
(NEW – OLD)/OLD
The mnemonic device I use is new comes first because your new stuff is more important than your old stuff. Then everything else is old. Dooon’t judge.
Here’s what it looks like in Excel …
How To Format
To format, just choose the percent formatting from Home > Number. And if you don’t want decimals (I rarely use them unless I have values under 5%), press the Decrease Decimal button until they’re sleeping with the fishies.
How To Get The Delta Symbol
To get the delta symbol in your Excel file, simply enter a capital D, select it, then change the font to Symbol. These get mangled in pivot tables though. I’m pretty sure that’s the only time I type it out.