The forcing notrump is a bidding convention in the card game of bridge.

In standard bidding, the response of 1 notrump to an opening bid of 1 of a suit shows 6 to 9 high card points and is non-forcing. Opener, with a balanced minimum, may pass the 1NT response and, if the opponents also pass, that will become the contract.

A partnership may agree that this bid is forcing for one round; if the intervening opponent passes, opener must bid at least once more. This guarantees the responder at least one more opportunity to bid or pass. This mechanism allows the partnership to use the 1NT response for a greater variety of hands: in particular, invitational as well as minimum responder holdings. The forcing notrump is used over major suits only; 1NT is always standard and non-forcing over the minor suits.

A bid of 1 forcing notrump shows 6 to 12 HCP, denies the ability to make a single raise (but not necessarily an invitational raise), and denies holding four spades if the opening bid was 1 heart.

Opener's rebid

Opener is forced to bid again as follows:

• 2 of original major shows a six-card suit
• 2 of a lower-ranking suit shows a second suit (which of necessity may be short?see below)
• 2NT is natural and invitational (showing about 18 HCP)
• 3 of a new suit (jump shift) is natural, normally agreed to be game-forcing, and shows about 19 points or more

When opener does not have a six-card original suit nor a four-card lower-ranking second suit, she will have to bid a short suit. Normally, she bids her three-card minor. If she has three cards in both minors, she bids 2 clubs.

If opener holds exactly four spades, five hearts, two diamonds and two clubs (and thus originally opened 1 heart), she bids 2 clubs (a two-card suit!). There is no point in showing the spades, because responder has denied holding four spades (having skipped the 1 spade response to bid 1 notrump). After a 1 spade opening, however, there is no distribution that would compel opener to rebid a two-card suit.

Some partnerships agree not to rebid a 2-card suit, preferring to promise 3+ cards. This allows responder to pass with 0,1 hearts and 4+ clubs. Instead, these partnerships rebid 2H (violating rule #1), or pass (if playing Semi-forcing Notrump.)

Responder's rebid

Responder categorizes her hand as either minimum (6-9 HCP) or invitational (10-12 HCP).

The minimum responder rebids are:

• 2 of opener's original major (shows two-card support)
• 2 of a new suit (shows a five-card or longer suit; some play a six-card or longer suit)
• pass denies either of the above (shows a distinct preference for opener's second-bid suit)

The invitational responder rebids are:

• 3 of opener's original major (shows exactly a three-card limit raise)
• 3 of a new suit (shows a six-card or longer suit)
• 2NT (natural)
• 3 of opener's second suit (shows at least four-card support)
• over a first suit of hearts unusual 2S may apply (see below)

Variation. There are more than one school of thought for responder's second call. The above text represents only one theory. Another widely utilized theory is the following:

With a minimum (6-9 support pts):

• pass (or raise) holding 5+ cards in the suit bid: exception - see false preference.
• bid openers first suit with 2 card-support: exception see false preference.
• pass holding 4+ cards in the current suit bid
• with a 6+ card suit with reasonable top-cards in the suit, bid that if it is between the current suit and 2 of openers suit. Example: (opponents passing) 1H-1N-2C-? 2D would fit this bid, but 2S would not (you would have bid 1S the first time, see unusual 2S)
• if none of these options work, usually pass with 3 in the current suit, otherwise bid openers first suit false preference (see below) may apply.

Further bidding

When responder rebids 2 of a new suit, opener should pass with a minumum and two or more cards in the suit. With a singleton or void in responder's suit, opener should rebid her original major. Responder may yet have a doubleton there and pass, or will be able correct to 3 of opener's second suit or her own good six-card (or longer) suit. In this way, the partnership is normally assured of at least a seven-card fit.

After an invitational responder rebid, opener is expected to pass (or sign off below game) with a minimum opening hand, or to bid game with extra values.

In line with the above Variation, when responder bids their own suit it is 'drop-dead', and Pass should is the expected response. However, with a good hand and 3+ card support a raise may be appropriate. Otherwise, the only reason to bid should be a good hand with 0 cards in the bid suit, and extra length in one of the first 2 suits, as partner has at most 1 card in our major and 3 cards in our minor.

Tactical raise

When responder has a very weak hand (0-4 points), but yet support for opener's major (three or more cards), standard bidding dictates a pass (because opener may have a very good hand and get overenthused after a single raise). This may allow the opponents to get into the bidding at a low level. Playing the forcing notrump, however, it is sometimes tactically advantageous to bid 1NT with this hand and then correct to 2 of opener's major. The 1NT bid tends to shut out the opponents and make partner cautious at the same time.

System implications

The forcing notrump is required for players using the 2/1 game forcing system, but may be used to advantage by other players as well.

False Preference

When in the maxi-minimum range (8-9 support points), and holding 2 cards in openers major and 5 cards in openers minor, you are worried about passing and missing game when partner has some extra-values. So you 'preference' to 2 of openers major. This keeps the bidding alive and allows partner to take another call even though your preference would in fact be for the minor.

When in the mini-minimum range (6-7 support points) and holding 2 cards in openers major and 4 cards in openers minor, you Pass. Even though the 'rule' says to preference to the major, the last thing you need is for partner to take another bid with extra values. By passing in a known fit, you hope to ensure the partnership a plus score.

Unusual 2S

Specific to the auctions: 1H-1N-2C and 1H-1N-2D. In these auctions responder is known to have fewer than 4 spades. Thus a call of 2S would have no sensible meaning. In these situations the raise of partner's minor is a slightly weaker hand, and the 2S bid is a 'power' raise to 3C. Usually based on 5+ of partners minor and invitational values.