🎓 A1Learner
🔍
0 of 43 lessons completed

Underpromotion

Underpromotion means promoting a pawn to a knight, bishop, or rook instead of a queen. It is rare, and it is chosen for a reason.

Underpromotion to a knight forks king and queen

The pawn moves from e7 to e8 and promotes to a knight. The knight attacks the king on g7 and the queen on d6. A queen on e8 would not attack both pieces.

FEN: 8/4P1k1/3q4/8/8/8/8/6K1 w - - 0 1

a b c d e f g h
8 . . . . . . . . 8
7 . . . . P . k . 7
6 . . . q . . . . 6
5 . . . . . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . . . . . K . 1
  a b c d e f g h

Underpromotion to a knight survives

The pawn moves from c7 to c8 and promotes to a knight. A queen or rook on c8 would be captured by the king on a8. The knight on c8 is safe, and the game goes on.

FEN: k7/2P5/1K6/8/8/8/8/8 w - - 0 1

a b c d e f g h
8 k . . . . . . . 8
7 . . P . . . . . 7
6 . K . . . . . . 6
5 . . . . . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . . . . . . . 1
  a b c d e f g h

Key points

  • A pawn usually promotes to a queen, because a queen is strongest.
  • A knight promotion can give check where a queen cannot.
  • A knight promotion can fork a king and a queen.
  • A rook promotion can avoid a stalemate a queen would cause.
  • A knight promotion can survive where a queen would be captured.
  • Underpromotion is worked out, not a trick for its own sake.
  • Always ask what the queen promotion would do wrong before you underpromote.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Rust Playground

Exercise

White to move. Which promotion forks the king on g7 and the queen on d6?