How long do I have to sue a debt collector for harassment in California?

A full year, counted from the date of the specific incident, is what both the federal statute and California's own version give you, the state deadline lives in Civil Code section 1788.30.

Here's the part that surprises people: it's not one clock for your whole ordeal, it's a fresh one for each individual incident. Say the harassment started two years back but one more call happened last month, that recent call can still be timely on its own even though the earlier pattern is long past its window. Track dates for each incident separately rather than treating the situation as a single ongoing complaint.