When does Christmas finish?

I know traditionally the christmas tree needs to come down on the 12th night or you will have bad luck. But when do you take down yours? I was looking at ours today and couldn't decide whether it is still christmas or the start of the new year celebrations. This time of year there always seems to be a lull. Everyone is tired from all the Christmas shenanigans and are recharging their batteries ready to send the old year out with a bang and great the new year. Although I will be at home as usual watching tv as we have our nephew over to stay.......again.