Distance to mate

Distance to mate, abbreviated DTM, expresses how far a position is from forced checkmate. In a tablebase, a precomputed collection that solves the covered positions for specified combinations of endgame pieces, the calculation is exhaustive. It is not an estimate produced by examining only selected continuations.

To obtain the number, the winning side tries to shorten the distance, while the defender tries to lengthen it without changing the theoretical result. DTM therefore describes the fastest mate against resistance that delays mate as long as possible.

A ply is one move by one side. Some tools report DTM in plies, while others use moves by the winning side or another documented convention. The interface's unit and sign must be checked before interpreting a number.

The DTM line is not always the most practical one. It may pursue the shortest mate without prioritizing a capture or pawn move that resets the fifty-move counter. DTZ, which targets the next reset, and DTC, which targets a capture or promotion, or mate if it comes first, are therefore used for different goals.