How Wide Should You Defend the Big Blind?

Against a 2.5bb button open you are risking 1.5bb to win the 4bb already sitting in the middle, so about 27% equity is enough to break even. Almost any two cards clear that bar against a button's range, which is why the big blind defends wider than any other seat at the table. The complication is that you play every one of those hands out of position for three streets, so the raw price overstates how wide you should really go. Here is how to turn the price into a defending range you can actually use.

The price the big blind is getting

You post 1bb before you see a card. That money is no longer yours — it belongs to the pot — and the only live question is what your remaining 1.5bb buys.

A 2.5bb button open builds a pot of 4bb: the 2.5bb raise, the 0.5bb small blind and your own posted 1bb. Calling costs 1.5bb and makes the final pot 5.5bb. Your share of that pot is 1.5 ÷ 5.5, or roughly 27%.

Equity needed = your call ÷ the pot after your call. From the big blind against a 2.5bb open, that is 1.5 ÷ 5.5 ≈ 27%.

27% is an extremely low bar. Even 72o, the worst hand in hold'em, runs close to 30% raw equity against a wide button opening range. On pure pot odds, folding anything would be a mistake.

Nobody defends 100%, and the reason is the subject of the next section. If the arithmetic itself is unfamiliar, how pot odds work covers the general version — the big blind is simply the spot where the calculation comes up most often.

Why the price is not the whole story

Raw equity assumes you get to see all five cards. You do not. You act first on every postflop street, you cannot take a free card when you want one, and your opponent gets to decide the price on each street with full information about what you did.

That gap has a name: equity realisation. A hand with 35% raw equity that plays badly out of position might only capture a fraction of that 35% by the river, because you are forced to fold it on so many flops.

Which hands realise their equity matters more than which hands have the most of it:

• Suited hands realise well. Flush potential gives you a hand you can continue with confidently on turns and rivers, so J6s outperforms J9o despite the lower card ranks.
• Connected hands realise well. Straight potential does the same job, which is why 76s defends comfortably and K3o does not.
• Weak offsuit hands realise badly. K4o flops top pair and then has no idea whether it is ahead. That uncertainty is what costs you money.

So the practical bar sits above the 27% the price demands. Not by a fixed amount, and not by enough to justify folding half your range, but enough that the very bottom of the pot-odds-approved list is a loser rather than a marginal winner. That is the whole reason a solver defends around half of hands rather than all of them.

What raise size does to your defending range

Raise size is the single biggest lever on how wide you defend, and it moves the price faster than most players expect.

Open size	You call	Final pot	Equity needed
2bb	1bb	4.5bb	22%
2.2bb	1.2bb	4.9bb	24%
2.5bb	1.5bb	5.5bb	27%
3bb	2bb	6.5bb	31%
3.5bb	2.5bb	7.5bb	33%
4bb	3bb	8.5bb	35%

Against a 2bb min-raise you need 22%, so you continue with nearly everything — folding there is one of the clearest errors in low-stakes online poker. Against the 4bb opens common in live games you need 35%, and a large chunk of your offsuit hands genuinely becomes a fold.

The step from 2.5bb to 3bb looks small and is not. Four points of extra equity trims a meaningful slice off the bottom of your range, and it is why online 6-max games settled on smaller opens in the first place.

Who opened matters as much as the size

The price tells you what you need. The opener's range tells you what you have.

A BTN opens roughly 40-45% of hands in 6-max, so your K7s has real equity against it. UTG opens roughly 15-17%, and against that range the same K7s is dominated by half the hands that continue. Same price, completely different decision.

The shift is not only about how much equity you hold. Against a tight range you are also up against more hands that keep betting on later streets, so you realise less of the equity you do have. Both effects point the same way, which is why defence against early positions tightens more than the raw equity gap alone suggests.

The widest defence of all comes against a small blind open. Not only does the SB steal with a wide range, but you close the action and act last on every postflop street — the one spot where the big blind has position. Rather than memorising a width per seat, work from solver-built defence ranges for each opening position and size. The other half of that battle, playing the small blind, explains why the SB opens so aggressively into you.

Call or 3-bet

Defending is not one action. Every hand you continue with is either a call or a 3-bet, and putting a hand in the wrong bucket costs you as much as folding it.

3-bet the hands that flatting wastes. Big pairs, AK and AQ lose value when you call and see a low flop out of position. Raising builds the pot while you hold the equity edge, and it wins the pot outright often enough to matter.

3-bet a smaller number of bluffs. Suited wheel aces, suited connectors and hands with the right blockers make good semi-bluffs because they remove strong hands from your opponent's continuing range.

Call with the wide middle. Suited gappers, small pairs and weak broadways have the price to see a flop but not the equity to fight a raised pot. Against a small open the solver mostly flats these and only occasionally turns them into raises.

Getting the split right by hand is hard, so let a chart do it. Reading the big blind defence chart tells you whether a holding calls, 3-bets or folds against each opening seat and size, which is far more reliable than a remembered percentage.

Tournaments, antes and short stacks

The big blind ante changes the maths in your favour. With a 1bb ante posted by the big blind, a 2.5bb open builds a 5bb pot, your 1.5bb call makes it 6.5bb, and you now need about 23% instead of 27%. Defence widens accordingly.

Stack depth pushes the other way. At 100bb you have room to flat speculative hands and outplay people postflop. At 20bb there is nothing to imply, so the flatting range contracts and marginal hands become either 3-bet jams or folds.

ICM tightens things further. Near a pay jump, the chips you risk are worth more than the chips you win, and thin defends that break even in chips lose money in real terms. Fold more when busting is expensive.

The mistakes that cost you the most

Folding to min-raises. At 22% equity required, giving up your blind against a 2bb open donates roughly a big blind of dead money every time it happens.

Defending too wide against big opens. The 4bb live raise is not the same spot as the 2.5bb online raise, and 96o is a fold against it however tempting the price feels.

Ignoring the opener's seat. A range built for the button and applied to UTG is a losing range. Adjust the width, not just the size.

Calling and then surrendering. If you defend 50% of hands and fold to every continuation bet, the defence never had a chance to pay. Winning the money back after the flop is a separate skill, and playing the big blind covers that postflop side.

Defence width is not a number to memorise. It is a price, an opening range and a realisation penalty, combined. Get those three inputs right and the correct width falls out on its own.