The first day of Hanukkah depends on the year and begins at sundown, not at midnight.
First day definition
Hanukkah always begins on the 25th day of the Hebrew month of Kislev and lasts eight days. Because the Jewish day starts at sunset, the first candle-lighting and start of the holiday are at nightfall on that date.
Example for 2025
In 2025, Hanukkah begins at nightfall on Sunday, December 14, and continues for eight nights, ending at nightfall on Monday, December 22. On the civil calendar, that means the “first day” of Hanukkah is Monday, December 15, even though celebrations begin the previous evening.
