Cost per Install (CPI) Calculator

Understanding the cost per install (CPI) calculator — concept and principle

Cost per install (CPI) is the average advertising cost of getting one person to install your mobile app. App marketers use it to compare networks, creatives and countries, and to check whether paid user acquisition can be paid back by the revenue those users later generate. It works with any currency; the default example uses US dollars.

How it is calculated

CPI = ad spend ÷ app installs

• Ad spend: total cost of the app install campaign for the period.
• App installs: installs attributed to that campaign, normally counted as first opens by your attribution tool or the ad platform.

The principle

CPI is a specific case of cost per acquisition where the action is an install. Like other average-cost metrics, it spreads the whole budget evenly across all installs. An install on its own earns nothing, so CPI only becomes meaningful when paired with what an installed user is worth: retention, purchases, subscriptions or ad revenue per user. If the average revenue per installed user over a chosen period exceeds CPI, the campaign has paid back within that period.

Worked example

1. Inputs: ad spend $4,000, installs 2,500.
2. CPI = 4,000 ÷ 2,500 = $1.60.
3. If 20% of installers are still active after a week, the cost per retained user is 1.60 ÷ 0.20 = $8.00.

How to read the result

CPI differs widely by platform, country, app category and campaign goal, so compare like with like. A low CPI with weak retention can be worse than a higher CPI that brings engaged users. A practical check is payback: how many days of average revenue per user it takes to recover the CPI. Organic installs that appear at the same time are not counted in CPI and can blur the picture.

Common mistakes

• Dividing spend by all installs, including organic ones, which makes paid CPI look lower than it is.
• Comparing CPI across countries without comparing the revenue per user in those countries.
• Ignoring reinstalls and fraudulent installs that some tools filter differently.
• Optimising for installs when the real goal is purchases or subscriptions.

Frequently asked questions

Is CPI the same as cost per download?

They are usually treated the same, though some tools count an install only when the app is first opened, not when it is downloaded.

How do I know if my CPI is too high?

Compare it with the expected revenue per installed user over your payback window, for example 30 or 90 days.

What is the difference between CPI and CPA for apps?

CPI counts installs; CPA for apps usually counts a later action such as registration, purchase or trial start.

Sources: Paul W. Farris et al., Marketing Metrics: The Definitive Guide to Measuring Marketing Performance (Pearson)