What it means
Between install and signup sits onboarding — permissions, registration, first screen. This rate measures how many survive it.
Worked example
12,000 installs produce 4,700 signups. Install-to-signup = 4,700 ÷ 12,000 = 39%. Lifting it to 50% adds ~1,300 signups from the same ad spend — cheaper than buying more installs.
Why it matters
A low rate usually means friction in onboarding, a slow first load, or a mismatch between the ad''s promise and the app''s first screen. It is often the highest-ROI fix in the whole funnel.