Some years the Jewish calendar has 12 months and some years (7 out of 19) are leap years with 13 months.
Jewish months alternate between being 29 and 30 days long.
However, the months of Marcheshvan and Kislev sometimes both have 30 days (a full year), sometimes both have 29 days (a missing year) and sometimes follow the regular order with Marcheshvan having 29 days and Kislev 30.
As a result, Chanuka (which starts on 25 Kislev and lasts 8 days) sometimes ends on 2 Tevet and sometimes on 3 Tevet.
This year is a "regular" year; Marcheshvan has 29 days, Kislev has 30 days and Chanuka ends on 2 Tevet.
Source: Kitzur Shulchan Aruch 221:4
- Danny Sunday, 3 Kislev 5769
Please daven for a complete recovery for Tamar bat Naama - תמר בת נעמה