It depends on a number of factors, including how well it has been cared for before and after being cut, the species of tree, and the environment it is kept in. Generally, a cut Christmas tree can last up to four weeks with proper care. This includes regularly checking the water level in the tree stand, keeping it away from heat sources, and not exposing it to extreme temperatures or drafts. Additionally, choosing a fresh-cut tree from a reputable vendor can also help to extend its life.