Monthly Active Users MAU (also MAP "monthly active people")
How many distinct people used the product across a month-long window.
The fork, why two teams get different numbers
The word "monthly" is a window, and three windows are in live use.
A CALENDAR-month MAU counts distinct actives from the 1st to the last
day (finance and board decks lean here because it aligns to the fiscal
calendar). A ROLLING 28-day MAU counts distinct actives in the trailing
28 days ending today -- the consumer-social default, because 28 is
exactly four weeks and removes the day-of-week and month-length wobble.
A TRAILING 30-day MAU splits the difference and is what most product
tools show by default. The same product on the last day of February can
report three different MAUs, and none is wrong.
The trap
A rolling window makes MAU look bigger and smoother than a calendar month of the same product, so month-over-month "growth" can be pure window artifact when someone switches definitions between two board meetings.
- The full trap, worked on a real export
- Every formula variant, spelled out
- The reconciliation anchor, what to tie it to and when to refuse
Reference: Product-analytics convention (no governing body) · IAB/MRC audience-measurement conventions