Commonly a double is considered for takeout whenever one of the following conditions is met (but see balancing double below):

• Opponents have previously bid only one suit, and the player did not have chance to double that suit before.
• Opponents have previously bid two suits, and partner has passed.
• Opponents have found a fit.

Most common requirements to make a takeout double are:

• Shortness in the opponents' suit(s) - preferably two or less, three at most
• Length in each unbid suit - preferably four cards, at minimum three
  • Some partnerships play that the double of a major promises four or more cards in the other major
• High card point (HCP) strength of at least a minimal opening bid - 11 or more HCP
  • More high-card strength is required when opponents have bid on higher levels (e.g. preempted).

The most common treatment is that the fewer high card points the hand possesses, the more strict are the distribution requirements (i.e. opponent's suit(s) shorter and unbid suits longer). With stronger hands a common treatment is to double first, regardless of distribution, and then make your bid even when it differs from partner's bid:^[3]

• 16+ HCP and a good six-card suit can convert partner's bid to this suit
• 18+ HCP and a good five-card suit can convert partner's bid to this suit
• 19+ HCP balanced with a stopper in opener's suit can convert partner's bid to notrump
• Exception: 15-18 HCP balanced hands with a stopper in opener's suit usually make a 1NT overcall instead of a takeout double

Partnership agreement is required on the level to which Takeout doubles apply. A typical treatment is that a double up to the level of 4♥ is takeout, while doubles on higher levels are for penalties or "cooperative" (i.e. the partner is supposed to pass unless his distribution and/or strength indicates that playing a contract of their own on a higher level is a better prospect). However an alternative is to play takeout doubles even higher^[4] for several reasons:

• It is rare to hold a "true" penalty double (length and strength in opponent's suit)
• With highly distributional hands it is possible for both sides to have a making game
• Usually the preemptive bid is designed to be sacrifice (in the expectation that the penalty score will be less than the score for the making game or slam)

Sometimes a “shape” double can be made on less than 12 HCP and can be made with 9+ HCP but requires 4 cards in all unbid suits (if only 1 suit bid by opponents) or 5–4 in unbid suits (if 2 suits already bid by opponents)

Opponents pass edit

If the RHO passes, the advancer (the doubler's partner) is forced to bid and should make a descriptive bid indicating suit length, high-card strength and any stoppers:

• Showing the shape:
  • With a longest suit bid this
  • With 2 suits of equal length but different rank (1 major and 1 minor) favour the major suit (as this will typically score better whether in a part-score, game or slam)
  • With 2 suits of equal length and rank bid the stronger suit
  • With 3 suits of 4 cards bid the (better) major
  • With a balanced hand and at least 1 stopper in the opponent's suit bid notrump
  • With an opening strength hand and no clear strain, a cue bid of opponents' suit is often used to set up a game forcing auction and asking doubler to describe their hand
  • When advancer's best suit is the opponent's suit, the takeout double can be passed for penalties and this is described in more detail below
• Showing the strength when bidding a suit:
  • 0-8 HCP - bid at the lowest available level in a suit (an expression sometimes used is "no more than an Ace and a King)
  • 9-11 HCP make a jump-bid
  • 12+ HCP jump to game, or if the strain is unclear, a cue bid of opponents' suit is often used to set up a game forcing auction and asking doubler to describe their hand
• Showing the strength when bidding notrump:
  • 8-10 HCP bid 1NT
  • 11-12HCP bid 2NT
  • 13+ HCP bid 3NT

The strength requirements above are lowered when the partner is known to be stronger (e.g. an opponent's preempt is doubled), and raised when partner can be weak (as in protective position).

One conventional variation (Bungay Black Dog Double) is that 1NT shows 6+ points and the cheapest bid in a suit is a natural "weak squeak" denying 6 points.^[5]

Opponents bid edit

If the RHO bids advancer is not forced to make a bid so, if one is made, it is a free bid and different strength ranges are used although the guidance on showing the shape remains the same except for the availability of the double as a new bid:

• Showing the strength when bidding a suit:
  • 0-5 HCP pass
  • 6-8 HCP bid at the lowest available level (can compete at the 2 level)
  • 9-11 HCP jump bid or compete at the 3 level
  • 12+ HCP bid the game or cue bid the opponents' suit
• Showing the strength when bidding notrump:
  • 8-10 HCP bid 1NT
  • 11-12HCP bid 2NT
  • 13+ HCP bid 3NT

Typically doubles of notrump bids are for penalty, the exception is when opponents make a "dustbin" notrump bid:

In this case, responder is not showing a balanced hand but denying both support for opener and the values to make a two-level bid so a double is for takeout in this situation. However attention must be paid to the likely meaning of the 1NT bid. In this case, responder is likely to have long clubs so it will be safe for North–South to play in hearts or spades.

Spades would be considered a safe suit but East might have length in clubs or diamonds.

There are no safe suits, East might have length and strength in any suit below spades. In addition, opener might have a second suit but have decided against bidding at the two-level given responder's weakness. In addition, since East-West may not have a fit it is possible that North-South do not have a fit and my end up at the two-level doubled so will need to exercise caution when vulnerable.

Double can be for takeout even in later rounds of bidding. As before, it denotes support for unbid suits and, often, extra values. In general, any low-level double after opponents have bid a suit (especially if they have found a fit) and partner has passed is generally played for takeout:

• the opener himself can double for takeout in the second round of bidding, after the opponents have entered the auction and partner had (usually) passed
• also, an overcaller can second-round double as well, to show extra values and support for unbid suits.
• a first-round takeout doubler can make a takeout double again, with a strong hand (around 16+ points)

Balancing (protective) doubles edit

Balancing (commonly called protective in England) doubles occur when the doubler had to choose between passing and ending the auction or bidding again to reopen the auction. Distribution and strength requirements for a takeout double are lowered in this situation. A common expression is "borrow a King" meaning that the balancing doubler can add 3 points to their hand and then bid according to strength guidance. So in this case a balancing double can be made with as little as 8HCP.^[6] and in some situations as little as 6HCP.^[7]

South, holding ♠ Q863 ♥ 84 ♦ A85 ♣ K1054 can now double, expecting to find partner with strength and likely length in hearts, allowing him to pass for penalties or make a bid and this is a case for bidding with a little as 6HCP^[7] with the right holding, shortness in hearts is particularly important and 4+ in all other suits would be ideal.

Although the bidding is a level higher East-West have found a comfortable fit and will probably be happy to play there. This suggests that North–South also have a fit and should be very keen to enter the auction. Competing at the three level might be risky as the major auction says very little about the minor suit holdings of East-West. South should double with 10+HCP and shortness in hearts.

As above South should be keen to compete (assuming East - West play traditional methods rather than inverted minors) but the auction has suggested that east–west don't hold length in any other suits (and the majors in particular).

South, holding ♠ Q863 ♥ 984 ♦ K1085 ♣ AJ was not strong enough to double in the first round. However, he can expect the partner to have shortness in hearts and likely 4 cards in spades or diamonds, and thus make a balancing takeout double. Such doubles are more frequent on matchpoint scoring, where even a penalty of −100 for the failure to make 2♠ can be profitable against −110 or −140 that the opponents could score in 2♥.

West's double denotes shortness in spades and support for the other, unbid suits with a hand such as ♠ 7 ♥ AJ85 ♦ K63 ♣ AQ1052.

Reopening doubles once showed extra values as well. With adoption of the negative double, however (a takeout double by responder), responder must pass with length and strength in the opposing suit. In order to protect against such situations, opener is obliged to double even with thin values, whenever his distribution is suitable. Some pairs even require opener to act somehow; responder's pass is forcing.

This convention (also referred to as ELCD) can change the meaning of doubler bidding a new suit in some situations, for example:

This does not promise the extra values in diamonds but shows a hand with 5 diamonds and 4 spades and the values for a normal takeout double. In this case doubler would need to jump in diamonds to show the stronger hand. Some partnerships only play the convention in a sequence like this converting clubs to diamonds.^[8][9] The name is derived from the fact that doubler is converting partner's bid at the same level.

This sequence does show a strong diamond hand as doubler has converted at a higher level.

Some partnerships also play this convention when holding 5–4 in the majors but with a hand that is neither weak nor strong and, therefore, they cannot use a 2 suited bid (e.g. Michael's cue bid).^[10]

• Negative double
• Negative free bid
• Support double