Depending on where you’re from as well as where you’re currently living, you might be wondering why some countries celebrate Christmas on 24 December while others wait for 25 December, and which one is the right way to do it.

Growing up in Paris, I remember celebrating Christmas on both the 24 and 25 December, but then again, that could have been because of my family’s tendency to do things extra, no matter what. After I moved to London and stayed there for my first British Christmas ever, I found out that in the UK, most people celebrate Christmas on the 25. At the time, I didn’t think much of it, until I stumbled upon the divisive question online.

Shortly after, while speaking to a Danish friend who was asking me when I usually celebrate the actual holiday, I realised two things: one, I have no idea what the custom is in France, and two, people are highly involved in this superficial debate. That’s when I decided to really look into it.

In the Czech Republic, Germany, Switzerland, Austria, Norway, Denmark and Finland (and perhaps even more countries), Christmas Eve, which is on 24 December, represents the start of Christmas. While shops tend to stay open in the morning to accommodate last-minute shoppers, in the afternoon, people start getting together with other family members to have dinner and deliver presents under the tree when no one is looking.

The 25 December, meanwhile, was originally considered more of a religious holiday spent worshipping, which explains why people still celebrate Christmas the day before. Now, why start one day early, you ask? A Christian liturgical day always starts and ends at sunset. In Southern Scandinavia, for example, the liturgical day on which Christ was born by tradition starts at 5 pm on the 24 and ends at the same time on the 25 December.

Celebrating Christmas on the 25 would imply having Christmas dinner the day after the event, as the liturgical day ends when the sun sets on the 25. Christmas Eve is therefore celebrated on the 24, while Christmas morning is celebrated on the 25, which also explains my confusion as to why some people—meaning me and my family—celebrate on both days.

However, even this explanation is not completely correct. Whether people celebrate the holiday on the 24 or the 25 varies from one country to another, even within one region. Furthermore, in Russia, Ukraine, Belarus, Moldova, Georgia, and Armenia, people celebrate Christmas on the 7 January during the next year due to their churches using the Julian calendar. Mad, right?

Christmas Eve simply means the evening before a religious holiday, Christmas in this case. This tradition of celebrating a specific holiday in the evening leading to that day goes all the way back to the Jewish calendar, on which each numbered ‘day’ of any month is considered to begin and end at sundown rather than at midnight. Jesus was, after all, Jewish.

That explains why, for many, Christmas starts at sundown on 24 December. The 25 is then considered the ‘Holy day’, which is spent praying and resting—basically minding your own business.

As mentioned previously, some churches (mainly Orthodox churches) use a different calendar for their religious celebrations. In Russia, Serbia, Ukraine and other countries, they use the old ‘Julian’ calendar and therefore celebrate Christmas on 7 January. The Ethiopian Orthodox Tewahedo church also celebrates Christmas on the 7, which is the 29 of Tahsas in their calendar.

Most people in the Greek Orthodox church celebrate Christmas on 25 December but some still use the Julian calendar and so celebrate Christmas on 7 January too. Same applies to some Greek Catholics. In Armenia, the Apostolic church celebrates Christmas on 6 January 6.

There you have it, Christmas day can be celebrated on many different dates depending on where you live, which religious beliefs you hold, and long time traditions.