Why your Shopify BFCM sales data is probably wrong when compared to last year

Most analytics and metrics tools give you the ability to compare your data to either the previous “period” or the previous “year”.

The previous period is self-explanatory. If we look at, say, the 4 days from 25–28 November 2022 compared with the previous period, we will get the 4 days previous to that—i.e., 21–24 November.

But, what about the previous year?

Shopify (and many other analytics platforms) considers the “previous year” to be 365 days ago.

So, if we compare the same 4-day period from 25–28 Novomeber 2022 to the previous year, we will get 25–28 November 2021. That makes sense, right?

Well, sort of. But, depending on what you are comparing—and, in this example—it could be entirely misleading.

25–28 November 2022 is the Friday through Monday following Thanksgiving—or BFCM.

25–28 November 2021 is Thursday through Sunday—an entire day short of BFCM!

It’s immediately clear that this will have a significant impact on your comparison reporting when evaluating how you did this BFCM vs. last year.

In order to compare BFCM 2022 to 2021, you actually need to compare Friday to Monday of boths years—or 25–28 November 2022 vs. 26–29 November 2021.

This applies to other, more generic reports also.

Ecommerce and retail brands aren’t purely seasonal—if you send email or SMS campaigns and post to social media on a weekly schedule, you will likely have clear day-of-the-week patterns, as well. If you run your monthly reports as “last 30 days”, there will be times when you will likely have an extra high-volume day on one side of your comparison that will be missing on the other.

To get more accurate comparison reports—especially if you like “rolling” reporting periods—I suggest you look at using multiples of 7—last 7 days for the previous week, 28 days for the previous month, 84 days for the previous quarter, 168 days for the previous 6 months, and 364 days for the previous year. This will lead to all your periods covering complete weeks. Then, when comparing to the previous “year”, compare to the same period 52 weeks ago so the days of the week align.

Unfortunately, this isn’t possible in Shopify. But, it is possible in other reporting tools. (And, in fact, Google Analytics has an option to “match day of week”.)

Of course, there are exceptions to this. If you are measuring performance around major shopping events like Valentine’s Day or Christmas, you may well want to run a report for the 14 days leading up to the holiday—irrespective of the day of the week.

If you’re struggling with getting meaningful data out of Shopify and you’d like help setting up better dashboards or reports, I might be able to help you.

Subscribe to Galen King

Don’t miss out on the latest issues. Sign up now to get access to the library of members-only issues.