As long as you have some time left after the holiday, it's best to leave it up for as long as possible. Taking it down too soon can cause some people to feel a sense of loss or sadness, as the Christmas season is over. But if you have a lot of decorations to put away, it's important to take it down before it starts to get dusty or cluttered. Generally speaking, it's best to take it down before the new year, but you can always leave it up a bit longer if you wish.