Monthly active users, or MAU, counts the unique people who performed a defined action in your product within the last 30 days. Each person counts once, no matter how often they return. You decide what active means: opening the app, or completing a real task. That choice changes the number.
MAU works as a size measure for products people use repeatedly, such as apps, marketplaces, and tools. It answers how many real people touched the product recently, which a count of registered accounts cannot answer.
An example. You have 12,000 registered accounts. In the last 30 days, 3,000 unique accounts logged in and created at least one document. Your MAU is 3,000, which is 25 percent of registrations. If 600 people use the product on an average day, your DAU/MAU ratio is 20 percent, so the typical active user shows up on about six days a month.
The common error is a soft definition. If you count anyone who opens an email or loads a page, your MAU inflates and stops predicting revenue. Pick a definition tied to the value you deliver, write it down, and keep it stable. Changing it later makes every past month uncomparable.
A second error is stacking weekly numbers. Four weeks of 1,000 weekly active users is not 4,000 MAU, because the same people return. The true figure might be 1,600 unique people, or 3,500. You only know by counting unique identifiers across the full 30 days.
Foundor's generated business plan lists MAU among the projected metrics for products with recurring usage. Treat that figure as an assumption: write your exact definition next to it, and replace the estimate with real measurement once the product is live.
