stickiness

Stickiness measures how often the people who use a product in a month come back within it. The classic version divides the average daily audience by the monthly one:

$\text{Stickiness}_{\text{daily}} = \frac{\overline{\text{DAU}}}{\text{MAU}}, \qquad \text{Stickiness}_{\text{weekly}} = \frac{\overline{\text{WAU}}}{\text{MAU}}$

where the bar means the average over the days (or weeks) of the same month. A DAU/MAU of 20% says the typical monthly user is active on about 20% of days, roughly 6 days a month. It ranges from 1/30 (everyone comes exactly once) to 100% (everyone comes every day).

Unlike MAU, stickiness is a ratio of habit, so it doesn't rise just because marketing brought more people. That makes it useful for comparing segments, platforms or product versions of different size, and for spotting a feature that turns occasional users into regular ones.

It only makes sense at the product's natural rhythm. A chat app should be judged by DAU/MAU; a product people need weekly (splitting shared bills, grocery planning) by WAU/MAU; a travel booking app by neither, because users with one trip a year are perfectly healthy. Mixed audiences need care as well: when the share of low-frequency segments grows, overall stickiness falls even if nobody's behavior changed (a mix shift), so read it by segment.