Read them over six weeks and in margin, not over four days and in revenue. Black Friday shifts sales as much as it creates them, and its real result only shows in January, returns included.
The benchmark
Three numbers are enough: the combined margin for November and December compared with last year, the share of new customers in the promotion's orders, and the return rate on those orders, which settles several weeks later.
A brand that lives on gifting adds a fourth, on a yearly scale. At a winter accessories brand the authors work with, a few million euros in online sales, December brings in eight to ten thousand new customers, versus a few hundred in summer.
In the cohort from the previous winter, meaning customers acquired the year before, one in eight ordered again, and one in twenty came back the following winter.
The median customer value there is the price of a single product. For these customers, the useful repurchase window is the following winter.
The rule
Judge the promotion on two-month margin and on what the customers it brought in buy again: at 90 days for a brand with replenishment, at the following winter for a gifting brand.
Compare with the same two weeks last year; October is not a baseline. A consultant on the team reminded a brand she advises of this last November, when people were tempted to read the month too early:
"Even for sites that don't run a Black Friday promotion, the share of spending is higher in November. Christmas is coming, and people prepare their purchases ahead of time."
The steps
- The comparison. Put all of November and December against the previous year, in orders, revenue and margin.
- The split. Separate new customers from existing ones, which means tagging them at the time of the order.
- The end of returns. Wait for it before drawing any conclusion, because returns arrive two, three, sometimes six weeks later. A higher conversion rate and a lower basket can pass for a good Black Friday until the returns come in.
- The log entry. Note the offer, the dates and any incidents.
- The cohort. Follow the new customers through February, then meet again next November.
A sentence to say to your leadership on November 30, adapted to your dates:
"The Black Friday verdict comes on January 15, returns and repurchase included."
The trap
This year, don't compare your conversion rate with Black Friday 2025.
Shopify changed how it measures sessions between September 21 and 23, 2026, without restating the history: the two rates no longer rest on the same count, and the year-over-year comparison on sessions stays broken until September 2027.
Compare orders, revenue and margin, whose definitions haven't changed.
And don't take that week's conversion rate as your new baseline: it will fall back.
In late 2025, a customer relationship software vendor measured on its own base that only 4% of customers acquired on Black Friday 2024 had bought again within the year, six times fewer than an ordinary new customer.
