Perpetual check, and why it is not really a rule

One player checks, the other has one square, the first checks again, and there is nothing to be done about it. It is the most common way a losing position turns into half a point, and it is not in the laws of chess.

Not a rule
Draws by repetition
Saves lost games

Perpetual check is a sequence of checks the defender cannot escape, played by a side who would otherwise lose. It is not a rule and it has no entry in the laws of chess. The game is drawn because the position repeats three times, or because the defender accepts that it will and offers a draw.

A forced one, checked move by move

A rook up, and one legal move

Black is a whole rook up and would win easily if the game continued. Black is also in check from the queen on g6 and, according to the engine, has exactly one legal move on the board: Kh8. The rook on f8 is Black's own piece and blocks the escape square.

The shuttle

The king goes to h8, the queen swings to h6 and checks down the h-file, and the king has one legal move again: back to g8. Then the queen returns to g6. Four half moves later the position is identical, character for character, to the one it started from.

1...Kh8 2.Qh6+ Kg8 3.Qg6+

Exactly the starting position, with Black to move and in check. Black can do this twice more and claim the draw, or White can, and neither player can deviate: Black has no other legal move at any point.

That is what makes it a draw. There is no rule saying "perpetual check draws". The position simply occurs three times with the same player to move, and threefold repetition does the rest.

When to look for it

When you are losing. This is the main one. A position where you are a piece down and your opponent's king is exposed is a position to check for perpetuals before you resign.
When your attack has run out. Sacrificing two pieces and finding the mate is not there does not have to be a disaster if the checks keep coming.
When your opponent's king has no shelter. A king dragged out to the middle is a king that can usually be checked forever, even by a lone queen.

And how to avoid allowing one

Give the king air before you need it. A king with two flight squares instead of one is much harder to check repeatedly, so pushing a pawn for luft is a defensive measure against perpetuals as well as against back rank mates. The other habit is counting your opponent's checks before you grab material: if the answer is "they have three and none of them lead anywhere", take the piece.

Black to move. The position looks lost. Find the move that saves it.

Show the answer

62.Qd6+ 62...Qxd6+ 63.Kxd6 63...f4

The line ends with the pattern paying off in material. The position is from a real game on Lichess, rated 605 in their puzzle pool, and it is one of the positions in the Defending skill in the trainer.

Questions people ask

Is perpetual check a draw?

Yes, in effect, but not by its own rule. The game is drawn because the same position occurs three times, which allows either player to claim threefold repetition, or because the players agree once it is obvious. The laws of chess contain no rule called perpetual check.

How many checks make a perpetual check?

There is no number. What matters is that the position repeats three times with the same side to move, which usually means the checking sequence has gone round twice. A run of ten checks that never repeats a position draws nothing.

Can you refuse a perpetual check?

You can decline to walk into the repetition by playing a different legal move, if you have one. In a genuine perpetual you do not: every check leaves exactly one legal reply, which is why it is called perpetual.

Perpetual check sits under How a game ends in the reference. Nearby: