Originally posted by AThousandYoungAnd when the queens are off by move 7. . . it's endgame?
One definition I've heard is the endgame starts when the Queens are off the board. I don't necessarily agree or disagree, but it's a good rule of thumb for a quick evaluation.
I think the best time i would officially call it an endgame is when the king comes out of hiding and plays a significant role.
For a full definition, I'd go with this on a first try:
Opening ends when the players have developed their pieces and begun combinational attacks or threats. Endgame begins when the combinations and mating threats lose most of their significance and the emphasis moves to Queening Pawns.
Sometimes people start combinations before being fully developed. (I define fully developed as having all minor pieces off the back rank and the King either castled or moved off the back rank, in a worst case scenario). In this case, if the threats are strong enough, it's middlegame. If they can be easily warded away while the defender continues to develop, then it's still opening.
Generally the possibility of combinations and mating attacks decreases drastically once the Queens are off the board. This is where the "Qs off the board" rule of thumb comes from.
Like I said, I don't necessarily 100% agree with it, but it is one of the signs to look for.
As someone previously pointed out, the stages of a game shouldn't be put in neat boxes. It leads to bad decision making. The game flows like a river or a life. You may be old but you can still go out a kick up your heels once and a while. If you think in categories, then you say, "I'm too old to do this or that, or I'm too young." On that same note, you might say, "I'm in the endgame, most of the pieces are off the board so I shouldn't expect combinations," but they happen! To use another metaphor (a golf one this time), play the ball where it lies. Treat every position as unique and try to find the best possible move. Hope this helps.