(EXPLAINER) Hanukkah falls a little later than usual this year — and it’s causing all kinds of headaches for interfaith couples and for interesting calculations for those curious about how time is measured.

This year, the start of Hanukkah coincides with Christmas Day. The eight-day celebration begins on Dec. 25 and continues into the new year.

Hanukkah — known as “the festival of lights” — is a time of reflection and celebration for Jews across the world. Typically, the miracle of Hanukkah is celebrated in early to mid-December, though the date varies each year depending on how the Hebrew calendar aligns with the solar calendar.  

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This year, Hanukkah’s start, at sundown on Dec. 25, coincides with Christmas Day. The eight-day celebration lasts for eight nights and ends on Jan. 2, 2025.

This is the opposite of what happened this past spring when Easter and Passover — two holidays that often overlap – fell about a month apart.

Why is Hanukkah so late this year?

Leap year is a very large part of the reason.

Just as the secular leap year corrects a problem in the Gregorian calendar, the Jewish version corrects a problem in Judaism’s largely lunar-based calendar.  

The Jewish calendar’s leap year is more complicated than adding an extra day to the end of February every four years to make up for the Earth’s rotation. Instead, to coordinate the traditional lunar year with the solar year, the Jewish calendar created a system of 19-year cycles (during which there are seven leap years).

Instead of adding a day, the Jewish calendar tacks on a full month — a second Adar — to the year.

How often have Christmas and Hanukkah coincided?

The holidays have coincided many times.  

However, since 1900, there have been only four occasions that the first night of Hanukkah began on Christmas Day: 2005, 1959, 1921 and 1910. The fifth takes place this year.

That means many U.S. homes will feature both Christmas trees and menorahs in the coming weeks.  

How many American families celebrate both holidays?

Exact numbers are hard to pin down.

Hanukkah almost always falls in the same month as Christmas – sparking a “December Dilemma” for many interfaith families. Jewish families, meanwhile, find that “the festival of lights” is very often forced to compete in the larger culture with Santa Claus and the Christmas season.    

The number of Jews in the U.S. has been estimated to be between 7.5 and 7.6 million, which is about 2.4% of the total population.  

A 2020 Pew Research Center survey found that 42% of Jewish people in the United States who are currently married have a non-Jewish spouse. The study also found that 28% of intermarried couples raise their children with a Jewish religious identity.  

In 2019, an Associated Press/NORC survey found that 92% of Americans will celebrate Christmas, 5% will celebrate Hanukkah and 3% will celebrate Kwanzaa. Five percent will celebrate more than one holiday.

Clemente Lisi is the executive editor of Religion Unplugged. He previously served as deputy head of news at the New York Daily News and a longtime reporter at The New York Post. Follow him on X @ClementeLisi.