For a mobile app, user acquisition cost is the spend required to acquire an install, trial, or paying user. Divide campaign spend by the matching number of users, then compare revenue from that acquired cohort with the same spend to find payback.
What is user acquisition cost?
User acquisition cost (UAC) describes what you spend to bring users into an app. The useful number depends on the outcome you want to buy: an install, a trial start, or a first payment.
For paid acquisition, match campaign spend to users attributed to that campaign. Including organic installs in the denominator understates campaign CPI.
How to calculate CPI for an app
Cost per install (CPI) is campaign spend divided by installs attributed to that campaign over the same period. If a campaign spends $S and brings N attributed installs, CPI is S ÷ N. Use the campaign's reported install count; do not substitute total downloads or store-page views.
ActivationPal's mobile app analytics can show Apple Ads spend, installs, and CPI alongside app event and revenue data. Its Apple Ads card includes a campaign split and ads-attributed revenue when Apple Ads is connected; see the Apple Ads setup and metrics. These figures help check acquisition cost against app outcomes, while the calculations below require matching the same acquired users.
Cost per trial and cost per paying user
Cost per trial is campaign spend divided by unique trial starters among its attributed installs. Cost per paying user uses unique first-time payers from that same acquired group. Count users, not trial or purchase events.
Follow the acquired users long enough to observe trial starts or first payments. App-wide outcomes cannot serve as campaign denominators when they include users from other sources. ActivationPal reports trial and purchase outcomes from connected revenue data, but its Apple Ads campaign card does not show campaign-level cost per trial or cost per paying user.
To see how acquired trials progress to paid users, use the same cohort discipline described in measuring trial conversion rate.
How to calculate app payback
Payback is when cumulative revenue from an acquired install cohort reaches its acquisition spend. The first period revenue meets or exceeds that spend is the payback period.
Per user, divide cohort spend by acquired users, then compare that cost with cumulative revenue per acquired user. Keep the revenue basis consistent across periods. ActivationPal defines net revenue as revenue after refunds, VAT, and store fees.
The ARPU calculator calculates average revenue per user from your inputs. App-wide ARPU is not campaign-cohort revenue, so use revenue from the acquired users over time. ActivationPal shows Apple Ads spend and attributed revenue, but does not calculate campaign payback. Its app revenue analytics can help you monitor app revenue for the comparison.
Paid acquisition cost vs blended acquisition cost
Paid acquisition cost divides paid campaign spend by users attributed to those campaigns. Blended acquisition cost divides acquisition spend across channels by all new users, paid and unpaid, in the same period. Paid cost compares campaigns; blended cost describes the overall acquisition program.
Keep spend scope and outcome consistent when comparing periods; CPI and cost per paying user answer different questions.
What Apple Ads and Android attribution show
ActivationPal captures Apple Search Ads attribution through Apple's AdServices on iOS. With Apple Ads connected, the dashboard reports spend, installs, CPI, impressions, and ads-attributed revenue, with campaign detail. The attributed revenue joins attributed devices to purchases received through the connected revenue provider.
This view covers iOS, not Android campaign spend or CPI. For Android, use spend and attributed installs from your ad platform or measurement setup, then apply the same formulas to those users.