Clicks divided by impressions - the share of people who saw your ad and acted. CTR tells you whether the message is earning the click, which makes it the per-creative diagnostic: compare it across angles and hooks to find what resonates. Two cautions. First, CTR varies heavily by campaign objective, so judge it alongside CPA, nCAC and post-click conversion, never in isolation - a high CTR on traffic that does not buy is a decoy. Second, it is your creative-fatigue alarm: CTR dropping 15-20% from its peak while frequency climbs means the audience is cooked.
Benchmark. On cold Meta Feed, 0.9-1.5% link CTR is average for DTC, 1.5-2%+ is good and 2%+ signals strong creative; below 0.9% the creative or offer is not compelling. Rotate when CTR falls 15-20% from peak while frequency exceeds 3.0x.