How long is the longest possible chess game?

Now that is a long time. You would be pretty fed up if you accidentally timed out after about 40 yrs.

Cool question

I think 1550

30 pieces each removed @ the 50th move = 1500

+ 50 moves when only the kings are left

RE: the pawns promotions- it dont matter if they promote or not, the piece must go on the 50th move

The answer is 5,870.5

Did you take into account what happens after all the pawns are promoted, say to 4N's on each side and 4B's, where the B's of the same side all travel on the same color and the B's of opposite sides travel on opposite colors?

I didn't do it.

It is a 50 move timer that prevents the game from being endless. It resets every time you move a pawn

In a chess game, a full move consists of a white move and a black move. Together they count as 1. In certain puzzles (like proof games) the single moves are also counted. 2.5 Moves from the beginning of a game then means 3 white moves plus 2  black moves!

Even if they dont claim it will be after 75 moves

after 75 moves players have to accept a draw by force(75 move rule)