Watch time
The total time viewers spend watching a video. A primary signal in YouTube's recommendation algorithm and a key creator KPI.
Watch time has been YouTube's dominant algorithmic signal since 2012. Session-level watch time matters more than per-video time, which is why retention-optimised chapter structure and a strong 30-second hook are so prevalent. Viewers who read a SumTube summary first and jump to the chapter they care about log shorter watch time per video but higher session completion — the metric creators actually care about.