Where do people say "on Christmas"?

I'm an American, and I always use 'on' with a holiday, never 'at'. I've lived in different parts of the US and Canada, and I can't recall hearing a North American say 'at Christmas'. My impression is that this is very much a cultural difference in usage.

It seems to me that we only add 'day' if we want to clarify that we're referring specifically to December 25th, but often temporal context makes it clear enough that we don't need to specify. For example, if I ask someone who lives abroad whether they're going home for Christmas, they'll know I mean the holiday period and not just the day, since almost no one would travel internationally for a single day's visit. If my friend lives in the same town as her parents and I ask her whether she's going to her parents' house for Christmas, she will know I mean the day, since it's unlikely that someone would spend a week with their parents when they have their own home nearby.

This is something we're explicitly made aware of when teaching English to foreign students as we teach British English but need to be aware of American English so that they don't become confused and unsure of what is correct when they hear American English used.

Traditionally in British English, "at" is always used for festivities. "At Christmas", "At Easter", whereas "on" is always used for days and dates in both British and American English. Thus "On Christmas day" is considered correct in both British and American English.

Using "On Christmas" is a uniquely North American phenomena, regardless of whether the speaker is simply abbreviating the phrase "Christmas day" or referring to the entire festival season. It's rare to hear someone say "on Christmas" in the British Isles, the only exception being foreigners with American influenced English.

In North America the phrase "On Christmas" is often used to refer to both the festival season and to the specific day itself, and generally context is used to distinguish whether the speaker is referring to the day or to the whole season.

I will add, however, that I believe "at Christmas" is not unheard of in North America, and that while it may have lost ground to "on Christmas", "at Christmas" can still be heard in various regions. I also believe that you'll frequently find "at Christmas" in older American literature as "on Christmas" as only become accepted as correct in American English relatively recently.

It might be worth nothing that a lot of preposition are possible with "Christmas", for, over, during, they all work as well, and various dialects have slight differences in preference when it comes to which to use when.