Generally lower fares for Christmas Break if you leave at least by December 15th.. any later, you're paying double/triple.. Sounds like the dates moved earlier to December 14th or 13th this year, probably due to time of week..

Coming back you can afford a bit earlier, say the 5th, 6th, or 7th to get a really good deal as well.. if you're only allowed to do a certain amount of time..

If you have points, this is the high season to use your points, as you'll receive the most value out of your FFP.