# App Marketing Metrics Explained: CPI, CAC, LTV and ROAS

> Plain-English definitions and formulas for CPI, CAC, LTV, ROAS, retention and payback period, with a worked example for mobile app marketers.

Published 2026-10-12, updated 2026-10-15. URL: https://www.ottosocial.ai/resources/blog/app-marketing-metrics-explained

## Key takeaways

- CPI = ad spend ÷ installs; CAC = acquisition spend ÷ paying customers.
- LTV = monthly revenue per user × average lifetime; aim for LTV:CAC of about 3:1.
- Break-even ROAS = 1 ÷ gross margin.
- Better creative lowers CPI and attracts more qualified users.

Four acronyms dominate app marketing conversations. Here is each one, the formula and how to use them together.

## The metrics

| Metric | Formula | Question it answers |
|---|---|---|
| CPI (cost per install) | Ad spend / installs | How much does an install cost? |
| CAC (customer acquisition cost) | Acquisition spend / new paying customers | How much does a paying user cost? |
| LTV (lifetime value) | Average revenue per user x average lifetime | What is a customer worth? |
| ROAS (return on ad spend) | Revenue from ads / ad spend | What did each ad dollar return? |
| Payback period | CAC / monthly gross profit per user (revenue if margin is ~100%) | How fast do we earn it back? |

## Worked example

Suppose you spend $2,000 and get 800 installs. **CPI = $2.50.** Five percent of installs subscribe, so 40 paying users. **CAC = $50.** Each subscriber pays $12 a month for an average of 9 months, so **LTV = $108.** LTV to CAC is 2.2 to 1, and payback is about 4.2 months. Improving install-to-subscriber conversion from 5% to 7% would lower CAC to about $35.71.

## Which lever to pull

- High CPI: improve creative hooks and targeting.
- Low install-to-purchase: fix onboarding and paywall.
- Low LTV: improve retention and pricing.

## Why creative drives all of it

On TikTok and Reels, creative is the targeting. A stronger hook lowers CPI and attracts more qualified users. That is why teams test many hooks quickly; see [TikTok hook formulas](/resources/blog/tiktok-hooks-for-app-ads).

## Calculate yours

Plug your own numbers into the free [app ROAS, LTV and CAC calculator](/resources/tools/app-roas-ltv-calculator).

## Frequently asked questions

### What is a good LTV to CAC ratio?

A common rule of thumb is 3 to 1 or better, meaning a customer returns at least three times what it cost to acquire them. The right target depends on your margins and cash position.

### What is the difference between CPI and CAC?

CPI is the cost of an install. CAC is the cost of acquiring a paying customer, which includes the conversion from install to purchase and often non-media costs.