Slam Bidding: When to Bid, How to Explore, and How Not to Go Down

Slam bidding is where bridge gets expensive. Bid one and make it, you get a huge bonus. Bid one and go down, you’ve turned a making game into a disaster. The difference between 620 and -100 is one bad decision in the auction.

So how do you know when to go for it? And once you decide to explore, how do you make sure you’re not missing two aces? That’s what slam bidding is all about.

What Is a Slam?

A slam is any contract at the 6-level or 7-level. You’re committing to take 12 or 13 tricks. That’s not easy.

Small slam = bidding and making 12 tricks (6-level)
Grand slam = bidding and making all 13 tricks (7-level)

The bonuses are significant:

That’s on top of your normal contract score. Bid and make 6♠ vulnerable, you score 1430 (680 for game + 750 bonus). That’s more than twice what you’d score for making 4♠.

But miss it by one trick? You’re minus. The slam bonus becomes a penalty. This is why slam bidding requires precision.

When to Look for Slam

The old guideline is 33+ combined points for slam. That’s a decent starting point, but it’s not the whole story.

What you really need:

1. Enough power: Usually 33+ HCP, but distribution can substitute for points
2. Controls in every suit: You can’t afford to lose the first two tricks
3. A good trump fit: Usually 8+ cards combined, with some quality
4. Sources of tricks: Long suits, ruffs, finesses that work

Points alone don’t cut it. You can have 35 HCP and no slam if you’re missing two aces. You can have 31 HCP and a cold slam if you have perfect distribution and fit.

The Quick Test

When partner makes a strong bid, ask yourself:

• Do we have 33+ points?
• Do we have a solid trump fit?
• Are we missing quick losers (aces and kings)?

If the answer to all three is “probably,” start exploring. If any answer is “no,” think carefully before pushing past game.

Slam Exploration Tools

You can’t just bid 6♥ and hope for the best. You need to check for controls. Here are the main tools.

Blackwood (4NT Asking for Aces)

This is the most famous convention in bridge. When you bid 4NT (in the right context), you’re asking partner: “How many aces do you have?”

Responses:

• 5♣ = 0 or 4 aces
• 5♦ = 1 ace
• 5♥ = 2 aces
• 5♠ = 3 aces

If you’re missing two aces, you sign off at the 5-level or pass. If you have all the aces, you can ask for kings by bidding 5NT.

King responses (after 5NT):

• 6♣ = 0 kings
• 6♦ = 1 king
• 6♥ = 2 kings
• 6♠ = 3 kings
• 6NT = 4 kings

Example auction:

1♠ - 3♠
4NT - 5♥ (2 aces)
6♠ - Pass

You opened, partner made a limit raise. You have 2 aces yourself, partner shows 2, so you have all four. Bid the slam.

When NOT to Use Blackwood

This is critical. Blackwood tells you how many aces partner has, not which aces. If you’re missing an ace and have a void, Blackwood can mislead you.

Don’t use Blackwood when:

• You have a void (you might be missing an ace in your void suit and still have “all the aces”)
• You have a worthless doubleton (partner might have 2 aces but you’re still missing the ace in your weak suit)
• You haven’t agreed on trumps
• The 5-level might be too high (if you’re missing 2 aces, you can’t stop below game)

Gerber (4♣ Asking for Aces)

This is Blackwood’s cousin, used primarily after notrump bids. When partner opens 1NT or 2NT and you bid 4♣, you’re asking for aces.

Responses:

• 4♦ = 0 or 4 aces
• 4♥ = 1 ace
• 4♠ = 2 aces
• 4NT = 3 aces

Then 5♣ asks for kings.

Example:

1NT (15-17) - 4♣
4♠ (2 aces) - 6NT

You have 17 HCP, partner has 16, and all the aces. Bid the slam.

Control-Showing Cue Bids

This is the sophisticated method. Instead of asking how many aces, you show where your controls are. A control is a first- or second-round control: an ace, king, singleton, or void.

After you’ve agreed on a trump suit, a bid in a new suit shows a control in that suit (usually an ace or king).

Example auction:

1♠ - 3♠ (limit raise)
4♣ - 4♦
4♥ - 6♠

Opener bids 4♣, showing the ♣A or ♣K. Responder bids 4♦, showing control in diamonds. Opener bids 4♥, showing heart control. Now responder knows opener has controls in all three side suits and can bid the slam with confidence.

Key rules for cue bidding:

1. You show controls up the line (cheapest first)
2. Skipping a suit denies first-round control in that suit
3. You don’t cue bid in trumps (that’s your agreed suit)
4. A cue bid at the 5-level or above usually shows first-round control (ace or void)

This method is more precise than Blackwood because you know which controls partner has, not just how many.

Quantitative 4NT

Not all 4NT bids are Blackwood. When you bid 4NT without having shown a suit fit, it’s usually quantitative — an invitation to 6NT based on points alone.

Example:

1NT (15-17) - 4NT

This isn’t asking for aces. It’s saying “I have 16-17 HCP. If you’re maximum, bid 6NT. If you’re minimum, pass.”

Opener bids 6NT with 17, passes with 15, and uses judgment with 16.

The same applies after 2NT:

2NT (20-21) - 4NT

Responder has 11-12 HCP and is inviting slam. Opener accepts with 21, rejects with 20.

Key Factors for Slam

Points matter, but these factors matter more.

Aces and Kings

You can’t make a slam if opponents cash two tricks off the top. Aces and kings prevent that.

The Rule of 30: If you have 30+ HCP and all four aces, you probably have a slam.

But distribution matters. Sometimes you can make slam with 28 HCP if you have a source of tricks. Sometimes you can’t make it with 34 if you’re missing quick tricks in a suit.

Trump Quality

You need solid trumps. An 8-card fit missing the ace, king, and queen is dangerous. You might lose 2 trump tricks, and that’s game over.

Look for:

• 8+ card fit
• At least 2 of the top 3 honors
• No more than 1 trump loser

If your trumps are AKQJxx opposite xx, you’re golden. If they’re Jxxxx opposite xxx, you’re in trouble.

Sources of Tricks

Where are your 12 tricks coming from?

In 6♠, you might have:

• 6 spade tricks
• 2 aces in side suits
• 3 tricks from a long diamond suit
• 1 ruff

Count them. If you can see 12 tricks, bid the slam. If you’re hoping for a finesse and a 3-3 break and good luck, maybe stop in game.

Duplication

If you have ♥KQJ and partner has ♥A432, you’ve got duplication—those honors aren’t creating extra tricks, just reinforcing what the ace controls. Look for hands where your strength complements partner’s rather than duplicating it.

When to Bid Slam vs. Stop in Game

This is the million-dollar question.

Bid slam when:

• You have 33+ HCP and all key controls
• You can count 12 tricks
• You’re missing at most one control and can cover it with distribution
• The risk/reward favors it (IMPs or rubber bridge)

Stop in game when:

• You’re missing two aces
• You have 12 tricks but they depend on a finesse
• Trumps are weak
• You can’t identify where all 12 tricks are coming from
• You’re playing matchpoints and making 12 tricks is enough to beat the field

The Matchpoint Exception

At matchpoints, bidding slam is often wrong even when it makes. If everyone else is in game making 12 tricks, you get the same matchpoint score whether you’re in 4♠ +680 or 6♠ +1430. But if you go down in slam, you get a zero.

So at matchpoints, be conservative. Bid slams that are close to cold, skip the ones that need a finesse.

At IMPs or rubber bridge, take more chances. The upside of making slam outweighs the downside of going down, as long as it’s a reasonable contract.

Example Slam Auctions

Example 1: Simple Blackwood

You:
♠ AKJ76
♥ AQ3
♦ K2
♣ K54

Auction:
You: 1♠
Partner: 3♠ (limit raise, 10-12 points, 4-card support)
You: 4NT (Blackwood)
Partner: 5♥ (2 aces)
You: 6♠

You have 19 HCP, partner has at least 10, so you’re at 29+. With 2 aces shown, you have all four. Trump fit is solid. Bid it.

Example 2: Control-Showing Cue Bids

You:
♠ AQ1098
♥ K2
♦ AJ1098
♣ 2

Auction:
You: 1♠
Partner: 2♣ (game-forcing)
You: 2♦
Partner: 3♠ (spade fit)
You: 4♣ (cue bid, showing club control)
Partner: 4♦ (cue bid, showing diamond control)
You: 4♥ (cue bid, showing heart control)
Partner: 6♠

You’ve shown controls in all three side suits. Partner knows you don’t have two quick losers anywhere and bids the slam.

Example 3: Quantitative 4NT

Auction: 1NT (15-17) - 4NT - 6NT

With 16 HCP opposite partner’s 1NT, you invite slam. Partner accepts with 17 points, giving you the 33 needed for slam.

Example 4: Stopping Short

Auction: 1♠ - 3♠ - 4♠

With 16 HCP opposite partner’s limit raise (10-12), you have 26-28 total. Not enough for slam. Stop in game.

Common Slam Bidding Mistakes

Mistake 1: Using Blackwood with a Void

You hold:

♠ AKJ876
♥ —
♦ KQ1098
♣ A32

Partner raises spades. You bid 4NT, partner shows 1 ace with 5♦. Which ace? If it’s the ♥A, you’re wasting it because you’re void. If it’s a minor suit ace, you’re missing the ♥A and they can cash it.

Better: Use control-showing cue bids. Bid 4♣, then 5♦ if partner cooperates. If partner bids 4♥, you know they control hearts and can bid slam.

Mistake 2: Bidding Slam on Power Alone

You have 35 HCP between you and partner. Great! But if your trump suit is QJxx opposite xxx, you might lose 2 trump tricks. Or if you have ♦xx opposite ♦xx, opponents cash 2 diamonds before you get started.

Points are necessary but not sufficient. You also need controls and a solid trump suit.

Mistake 3: Forgetting to Count Tricks

Partner opens 2NT (20-21), you have 13 HCP. That’s 33-34 total, but count tricks, not just points. You might have 10-11 tricks, not 12. Invite with 4NT, don’t insist.

Mistake 4: Taking a Finesse for Slam

You have 11 tricks and need a heart finesse for the 12th. At IMPs, a 50% slam is often worth it. At matchpoints, be more conservative—if the field is in 4♠ making 12, bidding slam risks a zero for the same result.

Mistake 5: Bypassing 3NT

When exploring slam, remember 3NT might be easier than 5-of-a-minor. Don’t commit to a minor suit slam without considering whether notrump plays better.

Mistake 6: Ignoring Vulnerability

Not vulnerable, a 50% slam is worth bidding at IMPs. Vulnerable, the penalty is larger—be more conservative. Vulnerability affects both your slam decisions and potential sacrifices against opponents.

The Deep Principle

Slam bidding is a conversation, not a calculation. You’re checking: Do we have the power? The controls? The trumps? The tricks?

If any answer is “I don’t know,” keep exploring. Use cue bids, Blackwood, or quantitative raises. Don’t guess.

When in doubt, stop in game. A making game scores well. A failing slam is a disaster.

Good slam bidding isn’t about being brave—it’s about being thorough. Check your controls, count your tricks, and pull the trigger only when you’re confident.

That’s how you collect the big bonuses without the big minuses.