What is an Undercut in Gin Rummy?

Short Answer
An undercut occurs when you knock but your opponent ends up with equal or lower deadwood than you (after laying off cards onto your melds). Instead of you scoring, your opponent receives a 25-point undercut bonus plus the deadwood difference.

How Undercuts Happen

  1. You knock with some deadwood (e.g., 8 points)
  2. Your opponent reveals their hand
  3. Opponent lays off cards onto your melds
  4. After layoffs, opponent's deadwood ≤ your deadwood
  5. Opponent scores the undercut bonus!
Example

You knock with 8 deadwood. Opponent has 12 deadwood but lays off 2 cards (worth 6 points) onto your runs. Their deadwood drops to 6. Since 6 < 8, they undercut you and score: 25 + (8-6) = 27 points.

Undercut Scoring

How to Avoid Being Undercut

Why Undercuts Matter

The 25-point swing (you losing potential points plus opponent gaining bonus) can dramatically affect the game. A single undercut can erase several rounds of careful play.