You can say “Happy Hanukkah” any time during the eight days of the holiday, and also in the days just before it starts.
Basics
Hanukkah lasts for eight days, and it is completely appropriate to wish someone “Happy Hanukkah” on any of those days. Many Jewish sources also consider it fine (and normal) to use Hanukkah greetings in the week or two leading up to the holiday.
For the year 2025
In 2025, Hanukkah begins on the evening of Sunday, December 14 and ends on the evening of Monday, December 22. For that year, “Happy Hanukkah” is most appropriate from a bit before December 14 and anytime through the evening of December 22.
After it is over
Jewish etiquette guides say it feels strange to keep saying “Happy Hanukkah” after the holiday has finished, even though other December holidays may still be going. After it ends, it is better to just say something neutral like “hello” or another general seasonal greeting.
