Bidding 4NT or 5NT over a Natural NT Bid

Please brush up on the responses to a 1NT opener with a balanced hand before reading this post:
Bidding - Responding to 1NT with a Balanced Hand

4NT or 5NT are both unusual bids to make after Partner has bid some level of NT. It is much higher than you need to be in order to get the points for bidding a game. Yet it does NOT commit to a slam. Why would bridge players make this bid?

Say you want to play in some level of NT. You have a balanced hand and Partner has opened the bidding 1NT so they have a balanced hand. If you wanted to be in a game only you would just bid game.

If you wanted to be in a small slam only you would just bid the small slam.

If you wanted to be in a grand slam you would just bid the grand slam.

Bids like 4NT or 5NT show interest in slams but shows that you are not quite sure what level you want to commit to.

Since a bid of 4NT is lower we will keep that as invitational to 6NT but NON-FORCING.

A bid of 5NT is therefore FORCING to at least a small slam but invitational to a grand slam. This bid CANNOT be Passed or the small slam bonus will not be given.

Let's take this hand:

Hand
♠K9
♥Q86
♦KQ64
♣AQ82

Partner opens the bidding 1NT. You play your NT range as 15-17 HCP. You have a balanced hand so you don't mind playing in NT. You also have 16 HCP. What do you bid?

In order to make a game the partnership needs at least 25 HCP. But if the partnership has at least 33 HCP you have enough to take 12 tricks and can get a small slam bonus.

The problem here is that Partner could have 17 HCP. Together with your 16 HCP you have 33 HCP between the two hands. That is enough to bid and make a small slam. So maybe you should just bid 6NT.

But hang on. Partner can open 1NT with only 15 HCP. If Partner has 15 HCP together your partnership holds only 31 HCP. This is NOT enough to make a small slam.

You don't get a slam bonus unless you bid the slam. So you should bid the slam.

If you don't make the slam then you lose points. So you shouldn't bid the slam.

Hmmmmm. There needs to be some way to ask PARTNER if they opened on 15 HCP or 17 HCP. Let them decide.

This is your 4NT bid. A bid of 4NT is INVITATIONAL to a small slam. Partner is expected either to PASS or bid 6NT. No other options. That way if Partner has 17 HCP they will bid 6NT and you will get your slam bonus. But if Partner only has 15 HCP they can pass and play in only 4NT. You will still get your game bonus but you will not get too high in the bidding and go down in your contract.

Let's take another hand:

Hand
♠K9
♥AQ8
♦KQ64
♣AQJ2

Partner opens the bidding 1NT. You play your NT range as 15-17 HCP. You have a balanced hand so you don't mind playing in NT. You also have 21 HCP. What do you bid?

In order to make a small slam the partnership needs at least 33 HCP. But if the partnership has at least 37 HCP you have enough to take 13 tricks and can get a grand slam bonus.

The problem here is that Partner could have 17 HCP. Together with your 21 HCP you have 38 HCP between the two hands. That is enough to bid and make a grand slam. So maybe you should just bid 7NT.

But hang on. Partner can open 1NT with only 15 HCP. If Partner has 15 HCP together your partnership holds only 36 HCP. This is NOT enough to make a grand slam. You could be off an Ace!

You don't get a grand slam bonus unless you bid the grand slam. So you should bid the grand slam.

If you don't make the grand slam then you lose points. So you shouldn't bid the grand slam. Just take the sure thing and bid a small slam.

Hmmmmm. Again, there needs to be some way to ask PARTNER if they opened on 15 HCP or 17 HCP. Let them decide.

This is your 5NT bid. A bid of 5NT is FORCING to a small slam and INVITATIONAL to a grand slam. Partner is expected either bid either 6NT or 7NT. No other options. That way if Partner has 17 HCP they will bid 7NT and you will get your grand slam bonus. But if Partner only has 15 HCP they can bid 6NT. You will still get your small slam bonus but you will not get too high in the bidding and go down in your contract.

This makes sense over a 1NT opening bid. But this works in ALL auctions where one person in the partnership has bid NT showing a balanced hand with some point count range and no fit for a suit.

For example:

Opener	Responder
1♣	3NT
4NT	???

Responder has shown a specific number of HCP with a balanced hand. The number of HCP Responder needs varies according to the partnership. Right now they teach this as showing 13-15 HCP. Back in the olden days Responder would bid this with 16-18 HCP. There is no right or wrong answer here. But you DO need to make sure you know how many HCP Partner has when they make this bid. Plus (just like opening 1NT) Responder needs to have in the range they promise when they make the bid. If Responder has 17 HCP but their 3NT bid promises 13-15 HCP they are not allowed to respond 3NT. They need to make another bid.

So that tells you what 3NT means in the auction -- what does the 4NT bid mean in this auction?

It is INVITATIONAL to a small slam. Opener is asking Responder if they are at their MAXIMUM to bid 6NT. But if Responder is at their MINIMUM to just Pass. The values for a small slam are just not there.

What values would Opener need to make this 4NT bid?

It depends on what the NT range is.

Calculate how much Opener would need if Responder promises exactly 13-15 HCP for their 3NT bid. Remember you need 25 HCP to bid a game, 33 HCP to bid a small slam and 37 HCP to bid a grand slam:



Calculate how much Opener would need if Responder promises exactly 16-18 HCP for their 3NT bid. Remember you need 25 HCP to bid a game, 33 HCP to bid a small slam and 37 HCP to bid a grand slam:





Another example:

Opener	Responder
1♣	3NT
5NT	???

So what does the 5NT bid mean in this auction?

It is FORCING to a small slam and INVITATIONAL to a grand slam. Opener is asking Responder if they are at their MAXIMUM to bid 7NT. But if Responder is at their MINIMUM to just bid 6NT.

What values would one need to make these bids?

It depends on what the NT range is.

Calculate how much Opener would need if the 3NT shows 13-15 HCP. Remember you need 25 HCP to bid a game, 33 HCP to bid a small slam and 37 HCP to bid a grand slam:



Calculate how much Opener would need if the 3NT shows 16-18 HCP:





Yet another example:

Opener	Responder
1♣	1♠
1NT	4NT

So what does the 4NT bid mean in this auction?

It is INVITATIONAL to a small slam. Responder is asking Opener if they are at their MAXIMUM to bid 6NT. But if Opener is at their MINIMUM to just Pass. The values for a small slam are just not there.

What values would Responder need to make this 4NT bid?

To answer that question we first need to think about what Opener has shown. They must have a balanced hand. They rebid 1NT when they had other choices to make. So they should have a balanced hand. But they opened the bidding 1♣ NOT 1NT. If they had a balanced hand with 15, 16 or 17 HCP they would have opened the bidding 1NT. Opener should not have 15 HCP. If they had a hand TOO good to open 1NT (say 18 or 19 HCP) they would NOT have rebid 1NT. They would have rebid 2NT. Therefore Opener should have AT MOST 14 HCP. But they might only have 13 HCP (or even a good 12 HCP). That is their range.

Calculate how much Responder would need to bid 4NT in this auction knowing the 1NT rebid shows 12-14 HCP. Remember you need 25 HCP to bid a game, 33 HCP to bid a small slam and 37 HCP to bid a grand slam:





Not another example!:

Opener	Responder
1♣	1♠
1NT	5NT

So what does the 5NT bid mean in this auction?

It is FORCING to a small slam and INVITATIONAL to a grand slam. Responder is asking Opener if they are at their MAXIMUM to bid 7NT. But if Opener is at their MINIMUM to just bid 6NT.

What values would Responder need to make this bid?

To answer that question we first need to think about what Opener has shown. They must have a balanced hand. They rebid 1NT when they had other choices to make. So they should have a balanced hand. But they opened the bidding 1♣ NOT 1NT. If they had a balanced hand with 15, 16 or 17 HCP they would have opened the bidding 1NT. Opener should not have 15 HCP. If they had a hand TOO good to open 1NT (say 18 or 19 HCP) they would NOT have rebid 1NT. They would have rebid 2NT. Therefore Opener should have AT MOST 14 HCP. But they might only have 13 HCP (or even a good 12 HCP). That is their range.

Calculate how much Responder would need if the 1NT rebid shows 12-14 HCP. Remember you need 25 HCP to bid a game, 33 HCP to bid a small slam and 37 HCP to bid a grand slam: