The questions to ask first:

What counts as 'active'? Opened the app? Completed a core action (sent a message, played a song, placed an order)? Passive background sync? The same MAU number can vary 2-5x depending on this choice.
Over what window? Last 30 days from today? Calendar month? Rolling 30-day window vs. month-to-date shows very different shapes.
Timezone? Users in Tokyo hit 'last 30 days' at a different wall-clock moment than users in New York. Pick one canonical timezone (UTC or HQ-local).
Deduplication? If a user has multiple devices / accounts, do they count once or multiple times? Requires identity resolution.
Include whom? Employees, bots, test accounts?

A defensible definition:

"MAU = distinct authenticated user IDs who performed [core action] in the trailing 30-day window, timezone UTC, excluding internal test accounts and known bots."

Why this matters:

Different stakeholders anchor on different definitions. Finance wants paying users; product wants engaged users; marketing wants any signup. You'll report different MAUs to different people, and that's fine as long as each is labeled.
If two teams' MAU numbers don't match, it's usually because they're using different 'active' definitions. The right response isn't 'who's wrong' but 'let's align definitions.'

What's a 'core action'?

Facebook: originally 'visited facebook.com.' Now probably 'viewed a post.'
Spotify: played a track ≥30 seconds.
DoorDash: placed an order. (Active users who merely browse don't count.)
Notion: opened a page.

The choice reveals what the business considers 'using the product' — not just 'the app was open.'

Common trap: counting login events. Login is a precondition, not activity. Counting it inflates MAU with sessions where the user immediately closed the app.

Stakeholder framing: "Before I pull MAU, let's align on 'active.' If you want casual visitors, that's one number. If you want users who took a meaningful action, that's another. The gap is often 30-50%."

What counts as a Monthly Active User (MAU)?

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