When does the middlegame end and the endgame begin?

Question

Is there any specific point where the middle-game ends and end-game begins? E.g. after x number of pieces are exchanged, or say 40 moves, etc.

Answer 1

One old definition of the endgame was when the main objective is to "queen a pawn," (as opposed to other goals such as forcing an imminent checkmate).

Now there is an exception noted in the comments where one side will try to mate the other side's lone king with a king and two bishops, or a king, bishop and knight. But it's likely that one side obtained this material advantage by trying to queen extra pawns, and forcing the other side to trade pieces for them.

Answer 2

There isn't a clear-cut definition of endgame, or a set of criteria where you could draw a line and say "after this move, we have reached the endgame."

Quoting Glenn Flear in his excellent book Practical Endgame Play - Beyond the Basics:

The word 'endgame' is widely used and generally implies the final phase of the game (however long!), assuming that there already has been significant simplification. If we had to define the word more rigorously in terms of material then opinions vary. Some specialists consider all queenless positions to be endgames, others those where both sides have limited material, for instance less than queen and rook.

So basically, once the position becomes 'simplified' to the point where more often than not you are using your few remaining pieces (including the King) to try and queen a pawn, rather than organize an attack. Also included would be the end result of queening a pawn (or winning significant material), i.e. positions where you mate the King with only a few pieces on the board, like King and Rook vs. King.

Answer 3

The middle game starts as soon as the opening ends, and well, it is very easy to know when openings start and end, almost any opening (if not all) have names and are well known and stuided. But if I were forced to say an specific moment in time, I would say around the time where they start castling or exchanging serious material to gain position advantage.

However, the end game is harder to accurately say when it starts, my best guess will be somewhere where the kings start moving towards the center and players have usually no more than 2 minor pieces or 4 pawns. Anytime where it is possible to calculate the result using Endgame Tablebases.

It is also worth mentioning that the point where something starts and ends vary from game to game (e.g if the players decide to quickly exchange material they will get to the endgame pretty soon), and some games don't even have end games (or even middle games!) if they blunder or fall in traps.