New Minor Forcing

New Minor Forcing ("NMF") is this sequence of bids by partners: 1 - 1; 1N - 2 where, obviously, the 2 bid is the minor not bid by opener.

1-1; 2N-3 is also NMF over the 18-19 HCP 2N.

The purpose of NMF is to show that responder has 5 of the major he bid (since 1 could be bid over 1 with just 4 in the suit) and to ask opener to show if he has 3 of responder's suit.

In a BidBase deal, west had KJ963-2-K843-KT9 and the bidding, with east opening, went 1D-1S, 1N-??. With NMF deactivated, BB now bids 2S to show 5 spades, but it might also show 6+ spades. West could make a 2D raise of opener's diamonds, and east should then bid 2S with the delayed support just showing 3.

Playing NMF, instead of rebidding a 5-card spade suit, west would bid the unbid minor, which in this case is 2C. This also indicates a 5-card spade suit. The responses below not only show if opener has 3 spades, but several other bids are available to describe opener's hand.

If not playing Fourth Suit Forcing, 1-1; 1-2 is also NMF.

1-1, 1N-2 is also NMF even though it technically is not a "new" minor.

NMF is usually 10-11 HCP, but could be more, and a 5-card major (but could be a stronger hand with a 4-card major).  
In preparing the NMF Quizzes, BidBase dealt responder this hand: AQJT3 AQ4 JT652 -- with partner opening 1. 
The question is whether to bid NMF 2 or to show the 2nd suit with 3? Is the hand strong enough? At this point, I don't know, but I expanded the NMF specs from 10-11 HCP to 10+ and we'll see if something comes along to contradict that.

The new minor is artificial, asking opener to describe his hand as follows:

Example: 1-1, 1N-2, ...

1. 2 = Show 3-card support for responder's major.
2. 2 = Bid the other major with 4-cards.
3. 2N = Bid NT with a stopper in the other major. This is risky if the suit is shorter than 3 cards,
   even with Ax, so BB's 2N promises 3+ cards in the other major as well as a stopper.
4. 3 = Raise the new minor bid by responder with 4+ cards in that suit.
5. 2 = Rebid his own minor if none of the above bids is possible.
   This is a bailout bid and doesn't promise length.
   Alternatively, 2N could be used as the bailout without promising stoppers.
   Take the hand xxx-xxx-AKQT-AQx. Both 2N and 3C are equally distasteful.
   Perhaps a less distasteful bid is to open the hand 1N instead of 1.
   Adventures In Bridge uses 2N as bailout (2=5+ diamonds) and adds the following:
6. 3 = At least 5 cards and a maximum.
7. 3 = 4 hearts and a maximum
8. 3 = 3 spades and a maximum
9. 3N = balanced, 2 spades, maximum, and stoppers in the unbid suits.

Note that if the bidding starts with 1-1, 1N, opener is denying 4 spades, so if responder bids the unbid minor for NMF, 2 by opener would be an "impossible bid" for showing 4 spades. Therefore, 2 must be asking responder if he has a spade stopper for bidding NT. A minimum hand for this would be Qx-xx-Axx-AKQxxx.

Likewise, 3 could not be natural, so it must be a splinter with extras but only 3 spades:  x-KQx-KQxx-AQxxxx

Raising With 3-Card Support

Bidding 1N with only 3-card support is not mandatory. For example, with QJ9 AJ976 73 A85, and a strong 3-card spade holding, Bobby Wolff said in his Nov.7, 2019 newspaper column that he would raise spades.

In the Nov.2020 Bulletin, p.39 #5, with 1-, most experts said they would bid 2 here instead of the 1 the problem showed because after 1-1N, a bid of 2 shows extras "which we don't have".

If not playing NMF and knowing that opener would routinely raise with 3, and with a weak hand, responder can just pass 1 with 4 spades, knowing that a Moysian Fit often gets a top.

With more than a minimum, responder simply makes a bid indicating that he only has 4.  He could bid a second 4-card suit or without one, just bid 2N or with a game force hand, bid an artificial 4th Suit Forcing. Over any of these, opener can correct back to responder's major with 4-card support.

Two-Way New Minor Forcing

"New Minor" becomes a misnomer in this convention because after 1-1, 1N, 2 starts the NMF sequence with an invitational hand and 2 starts the NMF sequence with a game-forcing hand, regardless of the minor suit opened.

Some say that only 12 HCP is needed to make a game force, but this seems light when people often open with just 11-12 HCP and the point of NMF is that no fit has been found yet. Do you really want to be in game with no fit and as few as 23-24 combined HCP? So in BidBase, 14 HCP is the minimum.

The Sept.2019 Bridge Bulletin, page 63, says that "almost all experts play two-way NMF."

After 2 is a relay to 2 by opener after which responder will describe his hand.

For a complete description of bidding after 2, see Adventures in Bridge and/or see Vic's Views in the September and October 2022 issues of ACBL's Bridge Bulletin and/or Dear Billy in the Sept. 2018 Bulletin, p.63.

Also see Checkback Stayman.

BridgeGuys.com shows a couple of interesting options, including a jump in the unbid minor (after bidding of 1-1, 1N) to show a weak 4-6 in the major-minor. Opener would pass without a hand with extra playing strength such as top support for the long minor and stoppers for the other two suits, in which case 3N should make.

BridgeBum.com says  

Bidding a 4-card major is opener's top priority in case a 4-4 fit is available. When both a 4-4 fit and a 5-3 fit are available, the 4-4 fit is generally preferred because the 5-card suit can theoretically be cashed to provide discards.

With 12-13 points and 3-card support, opener should bid partner's suit at the 2-level. With a good 13-14 points, opener should jump raise. 

Adventures in Bridge suggests that after opener's response to the new minor, responder can jump in opener's minor to show slam interest in that minor since with no slam interest, responder could just bid 3N.  
In this sequence, responder does not necessarily have 5 of his major since the goal is to show either a game force or slam interest in the minor. So 1-1, 1N-2, 2-3 indicates just a 4-card major and usually 6+ diamonds. 
AiB's rationale for this sequence is that neither 2 nor 3 of opener's minor is forcing whether playing Inverted Minors or not whereas raising the minor is forcing after using New Minor Forcing. However, a jump-shift in the other minor (e.g.: 1-2 or 1-3) is forcing, although it denies a 4-card major.

New Minor Forcing after 1x-1y, 2N showing 18-19 HCP.

The column Parrish the Thought in the February and March 2021 ACBL Bridge Bulletin was about NMF after opener rebids 2N showing 18-19 HCP. The number 1 rule is that if responder does anything but Pass, you are in a game-force.

To stop short of game, you must pass 2N "no matter what the shape".

The gist of this is that when responder does not pass 2N, he is promising a hand that is 5=4, 4=5, 4=4 in the majors or one 5-card major.

Opener's first priority is to bid responder's major with 3-card support (e.g.: 3H after bidding of 1C-1H, 2N-3D) else 3 of the other major with fewer than 3 of responder's major and 4+ of the other major (e.g.: 3S).

If opener bids 3H in this example, responder's next bid if 3N shows 4 spades and 4 hearts because opener's 3H bid only promised 3 hearts and responder is looking for an 8-card fit.

With 5=5 majors, responder should bid 1S instead of NMF and then bid hearts. With 5=6, he should bid 1H first and next bid spades.

The odds of New Minor Forcing coming up for a pair in a 27-board tournament is about once in every 6 tournaments, according to the CardShark BidBase Practice program.