Most readers will be quite comfortable on how to proceed when their partner opens 1NT. He shows 15-17 balanced. You add your points and know right away if you are in range for a partscore, game invitation, game, slam invitation, or slam. You can use Transfers or Stayman.
But, it is not as comfortable to handle a 1NT rebid. After you read this article, it should be! In fact, when partner rebids 1NT, you actually know more about his hand than had he opened 1NT.
Why? Because he has already opened in his long suit and he has not raised your suit. You know he doesn't have 4-card support for you. If you have only 4 in your suit, you can rule that out as a place to play. For example, after 1-1-1NT, you know that opener has 4 or 5 diamonds and only 2 or 3 spades. He would have raised with 4 spades. He would not have rebid 1NT with a singleton. Of course, you also know his HCP range. He has 12-14. With a balanced 11, he should not have opened the bidding. With a balanced 15, he would have opened 1NT. Furthermore, if he has 14, it is not a great 14. Many 14's would be upgraded to 1NT. I recommend opening 1NT with: K2
. With those 10's, controls and the 5-card suit, this hand should not be considered "14." So, the upper range for a 1NT rebid is a "so-so" 14. Accordingly, you shouldn't be interested in game if you have a flat 10 or 11.
If you are 4-3-3-3 or 4-4-3-2:
With less than 11 HCP, you have an easy pass.
With a very good 11 HCP or 12 HCP, invite with 2NT.
With 13 to about 17 HCP, go directly to 3NT.
With 18+, explore slam.
Some notes about borderline invitations (11-point hands):
1) If partner opened in 3rd seat, he could be a little lighter than normal. It would be very unusual to invite in notrump in such a situation. I don't think I've ever produced this auction: P-P-1-P-1-P-1NT-P-2NT. If I had enough to invite, I likely would have opened the bidding.
2) If playing matchpoints, don't stretch for marginal games. Even if game is 50-50, it is no big deal to be in it.
3) If vulnerable at IMPs, you can stretch a bit. If you have an attractive 11, you can invite after partner's 1NT rebid. The vulnerable IMP game bonus is too tempting to pass up.
4) Take partner's declarer-play ability into account. In borderline cases, invite only if your partner is a strong declarer. If your partner's declarer play is not up to the level of the field you are playing in, just pass. Maybe game is decent, but your partner won't find the road to 9 tricks. Settle for +90 or +120 and you might beat a bunch of pairs who reach a tough 3NT and go down one. You don't have to tell your partner "I used Larry Cohen's advice--he said that since you are a bad player, I shouldn't invite."
5) Don't be a bean counter. When I say "11" I am just counting HCP. You have to take into account hand-evaluation. Do you have suits such as J109x or Q1098? Those are obviously worth more than Jxxx or Qxxx.
6) With a 5-card major: If you have no game interest, your only 2 choices are PASS or rebid your 5-card suit. If you have a singleton, or 5-4-2-2, I would always run from 1NT. If you are 5-3-3-2, I would base my decision on my doubleton. If it is a small doubleton and not in the suit partner opened, I would prefer to play in the major. Yes, it might be a 5-2 fit. Usually, though, I would be content to pass the 1NT rebid. If you have at least game interest, you can use new minor forcing.
7) With a 6+ card major. You are sure to have at least an 8-card fit (I don't advocate partner rebidding notrump with a singleton). So, you can sign-off in 2 of your major, invite with 3 of your major, or insist on game by bidding 4 of your major. If you want to investigate other options (not likely), you can use new minor to start.
8) Assuming you are using new minor forcing, use it only with invitational or better hands. For more details, read the article on new minor. If the response was 1, followed by 2 (a new suit), that is NF (example: 1-1-1NT-2).