“I typically don't like people to optimize their campaigns for purchases or trial complete — those tend to happen way too far out. If you're a 7-day trial, for Google to get that data back seven days later is just too much lag. Optimizing for those earlier signals — most of the time a start trial — is the right approach.”

Optimize for trial starts not purchases — subscription purchase events lag too far for UAC to learn

Google UAC's algorithm needs conversion signals within a short window to optimize bidding effectively. For subscription apps, final purchase events are delayed by the trial period — meaning the algorithm flies blind during the most critical early optimization phase. Setting the optimization event to 'trial start' gives faster feedback while still serving as a strong proxy for downstream revenue.