The performance of a store network is measured by the progress of indicators compared to a reference period (most often year - 1, or year - 2) it can be non-comparable NC (without any filter in term of store) or comparable and in this case we will use the abbreviation of LFL means Like For Like.
This notion is quite simple, it’s based on store and date.
a store is comparable if there is at least one sale or return or a Goal on both dates (current and historical).
One day comparison
To have a comparable date the comparison date used is the date of the previous period (Y-1, Y-2 or CY) with the equivalent weekday.
Example :
Thusday May 7, 2021 is compared in LFL to Thusday May 7, 2020.
Friday April 30, 2021 is compared in LFL to Friday May 1, 2020.
February 2021 from Monday February 1, 2021 to Sunday February 28, 2021 is compared to the period from Monday February 3, 2020 to Sunday March 1, 2020.
Comparison over a period
As part of a date period, ONLY the dates when the same store has sales on both days (current and historical) will be considered in the LFL.
Example :
We analyze the turnover of store X, from February 1 to 7 on Y vs Y-1.
Store X is open 5 days in Y: Tuesday, Wednesday, Thursday, Friday and Saturday.
Store X is open 3 days in Y-1 on the comparison dates: Monday, Tuesday and Thursday.
The LFL from February 1 to 7 will therefore have an LFL comparison based on only two days Tuesday and Thursday.