What is the layoff undercut rule?

After the opponent lays off, if their deadwood is equal to or less than the knocker's, it is an undercut. The opponent scores the difference plus an undercut bonus, commonly 25 points, though some rules use 10 or 20.

Can you lay off after knocking?

No. The knocker may not lay off cards on the opponent's melds. Only the opponent, after the knocker has laid down, may lay off deadwood cards on the knocker's melds.

What cards can you lay off on a run?

You can only add a card that continues the run in sequence and in the same suit. Aces are low, so nothing extends past a King. You cannot add a card in the middle of a run.

Laying Off in Gin Rummy: What the Rules Allow

Q: Can you lay off on gin?

No. When the knocker goes gin, meaning they knock with zero deadwood, the opponent cannot lay off any cards. The hand ends immediately with the gin bonus.

Laying off in gin rummy is the move that decides most undercuts and causes the most table arguments, yet the rule is simple once you pin it down. After a knock, the defending player may place unmatched cards onto the knocker's melds, and those cards stop counting against them. The core question is: can you lay off on gin? Yes, but only as the defender, only after a knock, and never when the knocker goes gin.

The Basic Sequence After a Knock

When a player knocks, the play moves through a fixed order. First, the knocker lays down all melds and unmatched cards face up. Then the defender lays down their own melds. After that, the defender may lay off loose cards onto the knocker's melds. This order is not optional. It is the foundation of the rule.

If the knocker has a set of three 7s, the defender can add a fourth 7 from their hand. If the knocker has a run like 5-6-7 of hearts, the defender can add a 4 or an 8 of hearts, or both. The defender acts second, and only they get this privilege.

Who Can Lay Off

The Defender Lays Off, the Knocker Does Not

The rule draws a hard line: the defender may lay off, but the knocker may not. After the defender has laid down melds, the knocker cannot touch them. The knocker cannot add cards to the defender's melds, cannot rearrange them, and cannot reduce their own count by doing so. This asymmetry is deliberate. It gives the defender a chance to reduce their total, which is the whole point of the undercut rule.

Why the Knocker Cannot Lay Off

If the knocker could lay off on the defender's melds, they could lower their count after seeing the defender's hand, breaking the fairness of the scoring. The knocker committed to their count when they knocked. The defender's layoff is a response, not an invitation for the knocker to improve their position.

What the Defender Can Do

Lay off any number of cards, as long as each card legally extends one of the knocker's melds. Add a fourth card to a set. Extend a run at either end. You cannot add a card to the middle of a run, and you cannot move cards between melds. Each laid-off card must fit the existing meld as it sits.

The Undercut and How Layoff Affects it

How an Undercut Works

The most important consequence of laying off is the undercut. After the defender lays off, both players count their unmatched cards. If the defender's total is equal to or less than the knocker's, the defender has scored an undercut. The defender then scores the difference between the two counts, plus an undercut bonus. The standard bonus is 25 points. Some tables use 10 or 20, so confirm the house rule before you play, but the principle is the same.

Layoff Creates the Undercut

Suppose the knocker knocks with 5. The defender holds 8 before laying off, but they shed three cards, dropping to 2. Now the defender's count (2) is less than the knocker's (5), so the defender scores the difference (3) plus the undercut bonus. Without the layoff, the defender would have lost by 3 points. This is why the move is so powerful and why it decides most undercuts.

Laid-Off Cards Stop Counting

Once you lay off a card, it leaves your hand. It sits on the knocker's meld, and you do not count it. This can turn a losing hand into a winning one, or at least reduce the damage. The rule is absolute: laid-off cards are removed from your total.

When No Laying Off is Allowed

Gin Blocks All Layoffs

Two situations forbid laying off completely. The first is when the knocker goes gin, meaning they knock with zero unmatched cards. The defender cannot lay off anything. The knocker has already won the hand. The defender's only job is to count their hand and pay the gin bonus. The second is Big Gin, going gin using all 11 cards. No layoff there either. The defender cannot add anything to the melds.

When a player goes gin, they have no unmatched cards, so there is nothing for the defender to reduce. Allowing a layoff would let the defender lower their own count, but it would not change the fact that the knocker scored zero. The gin bonus is already awarded. The rules simply remove the layoff.

Big Gin Works Differently

Big Gin is rarer and more spectacular, and the rules treat it specially. Because the player used all 11 cards, there are no melds to extend in the usual sense. The defender has no right to add anything. The hand ends immediately with the Big Gin bonus. This is one of the few times the standard layoff rules do not apply.

Legal Layoff Examples and Common Mistakes

Use these to check your own play.

Legal: The knocker has a set of three 9s. The defender adds a fourth 9.
Legal: The knocker has a run of 3-4-5 of spades. The defender adds a 2 of spades or a 6 of spades.
Legal: The defender holds two cards that fit different melds and lays off both.
Illegal: The defender adds a 5 to a run of 3-4-6 of hearts. The 5 is not in sequence because the run is not contiguous.
Illegal: The defender adds a card of a different suit to a run. Runs must be same suit.
Illegal: The defender adds a card to a meld after the knocker has already gone gin.

The most common mistake is trying to lay off on a run out of sequence or across suits. Aces are low, so nothing extends past a King. You cannot place a card above a King, and you cannot place a 2 below an Ace in a run that goes Ace-2-3, because Aces are always low.

House Rules and Variations

While the core layoff rules are standard, some playgroups use variations. The undercut bonus is the most common variable. Confirm it before you start a serious game. Some tables restrict layoffs to one card per meld, though the standard rule allows multiple cards on the same meld.

Another variation concerns whether the defender must lay off if they can. In standard play, laying off is optional. You may choose to keep a card in your hand if you prefer, perhaps to avoid giving away information. The rules do not force you to reduce your count. However, if you do lay off, you must follow the sequence and suit rules.

Remember that the knocker never lays off. If you are the knocker, your only action after the defender's melds is to wait for the count. This asymmetry is the heart of the rule, and it is what makes the undercut possible.