I am not an expert in this, but I know that Sam2 is correct.
However, every one hundred years the date moves forward by one day. Every four hundred years, the date does NOT move by one day. So the date will move three times every four hundred years.
When I was young, the siddurim said Dec. 3/Dec. 4, and since then it has moved up a day to Dec.5/6.
The obvious problematical issue of a gradual change in the date (in the time of Shmuel, the date was in mid-late November)is a topic for another discussion.
Living in Eretz Yisrael, I rarely think about it.