CPI Calculator
Cost per install is the toll a user-acquisition team pays at the app-store door. Enter what you spent and how many installs it bought — then add a budget to see how many more that rate would deliver.
CPI (cost per install) = app ad spend ÷ installs. It is the headline price of a new app user, the metric every user-acquisition campaign reports first. But CPI is only an entry fee: a cheap install that never opens the app is worse than a pricier one that retains and pays. iOS installs typically cost more than Android, and incentivised traffic can slash CPI while delivering users who churn. Read CPI alongside retention and post-install value, never alone.
CPI Calculator inputs and result
How to use this calculator
- Pull spend and installs from the same windowTake both numbers from one date range and the same set of campaigns. A CPI that pairs this month’s spend with last month’s installs is meaningless.
- Use attributed installs, not store downloadsCount installs your measurement partner credits to paid media. Raw store downloads include organic and inflate your apparent efficiency.
- Read the cost per installThe headline is what one new install costs. Compare it across campaigns and platforms — but never forget iOS and Android live in different price worlds.
- Add a budget to project volumeEnter a planned spend and the tool estimates the installs it buys at this CPI — the input for a user-acquisition forecast.
- Export for the UA reviewCopy a share link, drop the CSV into your growth model, or print a one-page summary for the acquisition stand-up.
RGM Expert Says
When we audit a mobile user-acquisition program, CPI is the first number on the whiteboard and the first one we argue about. A team will celebrate a falling CPI without noticing the cohort behind it stopped opening the app. We treat CPI as the price of a ticket, not the value of the trip — the honest read only arrives once you trace those installs to day-1, day-7 and day-30 retention.
The classic trap is incentivised and low-quality traffic. Offer-wall and bot installs can drop a CPI to pennies and gut your retention at the same time. We watch CPI and retention as a pair: if CPI falls while retention falls faster, the channel is buying you a vanity metric. The goal is the lowest cost per retained, paying user, which often means accepting a higher CPI from a cleaner source.
Platform context decides everything. Apple Search Ads installs behave nothing like Google App campaign installs, and iOS post-ATT measurement makes raw CPI comparisons across platforms genuinely unsafe. We benchmark each source against itself over time and judge new spend on blended payback, not on whoever is reporting the cheapest install this week.
How it works
CPI is the bluntest user-acquisition metric: divide what you spent on installs by the installs you got.
- App ad spend — paid UA media driving installs in the period.
- Installs — attributed installs in the same period; use MMP data, not raw downloads.
- Planned budget — optional future spend, converted to a forecast install count.
CPI says nothing about quality. Pair it with retention and post-install ROAS; see RGM’s cost per install deep dive.
Why a cheap install can be the expensive one
CPI is seductive because it is simple, and dangerous for the same reason. The number that actually decides whether user acquisition pays is not the cost of an install but the cost of a retained, monetising install. A $0.40 install that churns by day three is pure loss; a $1.50 install that stays for months and subscribes is a bargain. Optimising CPI in isolation quietly selects for the worst users you can buy.
The second issue is comparability. iOS installs cost more than Android, premium-network installs cost more than incentivised ones, and post-ATT measurement on iOS makes raw cross-platform CPI comparisons unreliable. Treat CPI as a within-channel trend line, not a leaderboard across channels with different economics.
Used properly, CPI is a planning input, not a trophy. Once you know your CPI and your downstream value — retention curves, in-app ARPU, install-to-paid rate — you can set an allowable CPI that still clears payback, then hold every source to it. That turns user acquisition from a race for cheap installs into a disciplined hunt for profitable ones.
How to read cost per install
There is no single ‘good’ CPI — it swings by platform, geography, vertical and source quality. Use public ranges to orient, then judge against retention and post-install value.
| Signal | What to watch | Why it matters |
|---|---|---|
| CPI by platform | iOS usually well above Android | Different audiences and auction dynamics; never blend blindly |
| Incentivised traffic | Very low CPI, poor retention | Cheap installs that churn destroy payback |
| Geo and vertical | Tier-1 geos and gaming run higher | Benchmark within the same segment, not across |
| The real KPI | Cost per retained / paying user | CPI is the entry fee, not the return |
What growth leaders say about installs
The vanity metric in mobile is the cheap install. The number that compounds is the retained user, and retention is a feature of the product long before it is a feature of the media plan.
Buy users you can keep. A lower cost per install that hides a worse cohort is not efficiency — it is a slower way to lose money.