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Payment and models

CPI (Cost Per Install)

Also called Cost Per Install, price per install, pay per install, PPI.

Short answer

CPI (Cost Per Install) is a payment model in which the advertiser pays a fixed amount for each installation of an app. Payment is triggered by the install, and many programs also require the app to be opened at least once.

Definition of CPI (Cost Per Install).

CPI belongs to mobile marketing and is a variant of CPA where the action is an app install. The amount is fixed per install and varies with market, platform and category – a game in a small language area costs something entirely different from a finance app in a large one. In return, the model makes the advertiser’s cost per new user predictable.

Installs are measured differently from purchases in an online store. On Android, the Google Play Install Referrer carries the source information through the install. On iOS, SKAdNetwork only provides aggregated postbacks, and without the user’s permission under App Tracking Transparency there is no device-level tracking. That is why a mobile measurement partner usually sits between advertiser and media.

The price covers an install, not a user. A large share of installed apps are opened a few times and deleted again, which is why many advertisers supplement CPI with a requirement for a follow-up action – a registration, a completed onboarding flow or a first purchase – before the campaign counts as profitable.

How it is calculated

CPI = total campaign spend ÷ number of installs

total campaign spend
everything paid to media and partners in the period, excluding VAT
number of installs
attributed installs, not the app store’s total download count

Example

Campaign spend
DKK 25,000
Attributed installs
1,000
CPI
DKK 25.00

A CPI of DKK 25 is only useful alongside the share of installs that are still active after a month.

CPI, CPA and what happens after the install

CPI is the cheapest and most uncertain of the mobile models. A CPA on a registration costs more per action but delivers users who have taken one more step. Paying for a first purchase costs more still and leaves almost no doubt about the value.

The comparison should therefore not be made on price per install, but on price per user who is still there after 30 days. A CPI of DKK 12 with 5 % remaining after a month is more expensive than a CPI of DKK 30 with 40 % remaining.

How it goes wrong

  • 01

    Incentivised installs are counted

    Installs obtained through offer walls and reward apps hit the target and disappear again. Require incentivised traffic to be labelled as such, and compare its retention with the rest.

  • 02

    CPI calculated against the app store’s download count

    The App Store and Google Play count every download, while the campaign can only attribute some of them. If the store’s figure is used as the denominator, CPI looks artificially low.

  • 03

    Retention is not part of the deal

    If payment is made on the install alone, the media partner has no reason to deliver users who stick around. A requirement for an action after the install shifts the incentive.

Frequently asked questions

What is the difference between CPI and CPA?

CPI is a CPA where the action is an app install. CPA is broader and can just as well be a lead, a registration or a sale. CPI is the most uncertain variant, because an install is not the same as a user.

How much does an app install typically cost?

The price varies greatly with country, platform and category. Get current quotes rather than relying on a general level, since figures from another category or another market rarely transfer.

How is an app install tracked?

On Android, the source is carried through the Google Play Install Referrer. On iOS, SKAdNetwork provides aggregated postbacks, and without the user’s permission there is no device-level tracking. That is why many advertisers use a mobile measurement partner to consolidate the measurement.

Is CPI relevant for a typical website affiliate?

Only if you work with app advertisers. If the program sells on a website, payment is made for sales or leads, and then CPS and CPL are the models to compare.

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