What is an interstitial ad in mobile apps and games?

Short answer. An interstitial ad is a full-screen ad that covers an app's interface until the user closes it or taps through. Publishers show it at natural breaks, such as between levels of a game, and it is a slot where in-app video, playable and end card creative often runs.

The definition

Google's AdMob developer documentation says: "Interstitial ads are full-screen ads that cover the interface of their host app. They're typically displayed at natural transition points in the flow of an app, such as between activities or during the pause between levels in a game." When one appears, "the user has the choice to either tap on the ad and continue to its destination or close it and return to the app."

AppsFlyer's glossary uses the term more widely, covering apps and the web: interstitials "are full-screen, interactive ad placements that are served at natural points along a user's journey in an app, mobile website, or desktop site."

Two sides of the same slot

For a publisher, an interstitial is a monetization decision. Google's AdMob policy guidance says interstitials "are best suited for apps with linear user experiences" with "very clear starting and stopping points", and warns that a full-screen ad "can result in accidental clicks if placed at the wrong time."

For an advertiser, an interstitial is a few seconds of a full screen and someone's attention between two things they chose to do. The same AdMob guidance notes that "some interstitial ads may have up to a 5-second delay before providing a close option. If high-engagement ads are enabled, interstitial video ads may have up to a 12-second delay." Those first seconds are the part every viewer sees.

A worked example (illustration)

These numbers are made up. An ad runs 100,000 interstitial impressions and produces 1,000 installs. That is 10 installs per thousand impressions (IPM). If a new opening lifts it to 1,300 installs on the same impressions, IPM is 13, and the creative change alone moved the result. Because the format is full screen and the audience is fixed by placement, interstitial IPM is a fairly clean read of the creative.

What a good or bad reading tells you

A high click rate with a weak install rate on an interstitial is worth checking before celebrating: on a full-screen unit some taps may be accidental, which is exactly the risk Google flags to publishers. A low IPM with decent completion usually means the ad was watched but did not give a reason to act, often a problem at the end screen rather than the opening.

In games and in consumer brands

Our read: game advertisers know this slot well because their players live in it. Consumer brands buying in-app inventory are showing their ad in the gap between someone else's game levels, to a person mid-session. The ad has to make sense to someone who did not come looking for it.

Common mistakes

• Opening on a logo or slow intro when the viewer may be able to close after a few seconds.
• Judging an interstitial on clicks alone, given the accidental-click risk.
• Forgetting the end screen. On many networks the video is followed by an end card, which is where the tap happens.

Flixr's view

We treat the interstitial as one canvas with three parts: the opening seconds, the video or playable, and the end card. Each is a separate variable worth testing. Our taxonomy of hooks covers the opening; our end cards guide covers the close.