21 March 2026 · United Kingdom

Cohort windows under UK store seasonality

A 28-day window is not a personality. In Britain it is a collision with bank holidays, payday, and a January that pretends to be a new self.

Vendor defaults love 7, 14, and 28. They look scientific. They also stride across Easter, late-May weekends, and the week the country collectively decides to cook at home. If your grocery app’s “habit” is measured in a window that includes a bank holiday and excludes the following Tuesday, you will staff the wrong squad.

App Analytics in the United Kingdom has to treat the civil calendar as an input, not an inconvenience. We teach students to publish the clock beside the figure: UTC, Monday-start weeks, and whether Christmas Eve is a trading day for their category.

January is a listing event

Fitness, recipe, and budgeting apps inhale tourists in the first fortnight. If you fold them into resident cohorts, February looks like a tragedy. It is usually a return to the population you actually have. Split the families. Let January tourists have their own honest decay.

Payday is not a week

Some UK fintech surfaces move with last-Thursday or last-Friday pay cycles, not with ISO weeks. A cohort window that ignores payday will invent churn that is only cashflow. This is not advanced statistics. It is reading a payslip beside a chart.

Bring your calendar to the studio if you want a Pulse Reading Saturday spent entirely on windows. We will not sell you a 28-day religion.