In Dragon Ball Z Kai , the Cell Saga starts at episode 68. It begins with the episode “A Challenge from Cell! Androids 17 and 18” in most episode guides.

Quick note

Some sources split the Cell arc into smaller parts, so you may also see Cell Games Saga listed later, starting around episode 89.

Why the numbering can look different

Different guides sometimes label the Cell Saga versus the Cell Games Saga separately, which is why episode numbers can vary depending on the arc breakdown.

TL;DR: Cell Saga = episode 68 in Dragon Ball Z Kai.