Cost Per Install (CPI)

Cost Per Action (CPA) is a performance-based pricing model in which an advertiser pays only when a user completes a specific post-install action, such as making a purchase, starting a free trial, or subscribing to a service. Unlike CPI, which measures cost at the install level, CPA ties advertising spend directly to business outcomes further down the funnel. For subscription apps, common CPA events include trial starts, first subscription payments, or registration completions. CPA is particularly useful for evaluating the true efficiency of user acquisition campaigns, since an install alone doesn't generate revenue — what matters is whether the user converts into a paying subscriber. By optimizing toward CPA rather than CPI, growth teams can focus ad spend on channels and creatives that deliver users with higher intent and better downstream conversion behavior, even if those channels have a higher cost per install on the surface.

Cost Per Mille (CPM), also known as cost per thousand impressions, is an advertising pricing model where advertisers pay a fixed rate for every 1,000 times their ad is displayed to users. "Mille" is Latin for thousand. CPM is one of the most common buying models in digital advertising, particularly for brand awareness campaigns and display advertising. In the mobile app ecosystem, CPM is used both by app developers buying ads to acquire users and by app publishers selling ad inventory within their apps. For user acquisition, CPM campaigns are typically less performance-oriented than CPI or CPA models, since the advertiser pays for visibility rather than a specific action. However, CPM can be effective for reaching large audiences at scale and building brand recognition. For app publishers monetizing with ads, CPM represents the revenue earned per 1,000 ad impressions served — also called eCPM (effective CPM) — and is a core metric for evaluating ad monetization performance across different ad networks and formats.

The amount spent for each newly-acquired mobile app user over a given time period. Customer Acquisition Cost (CAC) for mobile apps refers to the cost that a business incurs to acquire a new user for their mobile application over a specific period of time. In other words, it is the amount of money spent to attract a user to download and install a mobile app on their device. Whether you are just embarking on your journey or navigating quite a while to create a successful mobile app, the Customer Acquisition Cost (CAC) must be at the forefront of your mind.

Paid installs, also known as non-organic installs (NOI), occur when a user downloads and installs an app after being exposed to a marketing campaign. These campaigns can take various forms of advertising, such as social media ads, display ads, video ads, or search ads, and are part of user acquisition efforts on paid and owned media.

Return on Ad Spend (ROAS) measures the revenue generated for every dollar spent on advertising. It is calculated by dividing total revenue attributed to a campaign by the total ad spend on that campaign. A ROAS of 2.0 means the campaign generated $2 in revenue for every $1 spent. ROAS is the most widely used profitability metric in mobile user acquisition because it directly connects marketing investment to revenue outcomes. For subscription apps, ROAS calculations must account for the time lag between ad spend and revenue realization — a user acquired today may not generate their first payment for 7 days (if they start with a free trial) and may generate revenue over months or years of subscription renewals. This makes "Day 0 ROAS" (revenue from immediate purchases) an incomplete picture. Growth teams track ROAS at multiple horizons — Day 7, Day 30, Day 90, Day 365 — to understand the full return curve. Target ROAS thresholds depend heavily on a company's margin structure: apps routing payments through app store billing (with 15–30% commissions) need higher gross ROAS than apps processing through web checkout to achieve the same profitability.