ARPPU stands short for “Average Revenue per Paying User,” and is a metric that estimates the amount of revenue a paying user generates over a period of time.
To calculate the ARPPU of an app, divide its total revenue by the number of paying users in the given time period.

ARPPU is vital for all apps that offer some kind of in-app purchases or subscriptions. It tells marketers and developers how much a paying user is worth to the business. Knowing this allows them to calculate how much they should spend to acquire a paying user.
Two metrics resemble ARPPU by name, but they are significantly different. These are ARPU and ARPDAU, so visit their glossary pages and learn more about them.