Blackjack: When to Double Down and When to Split Pairs

The short answer to blackjack when to double down: double a hard 11 against any dealer upcard except an ace, a hard 10 against a dealer 2 to 9, and a hard 9 against a dealer 3 to 6. In each case you’re more likely than usual to end up with a strong total, and the dealer is showing a weak or average card. Some soft hands (hands with an ace counted as 11), such as A,6 or A,7, are also worth doubling against a dealer 3 to 6.

For splitting, the rule to remember is: always split aces and 8s, and never split 5s or 10s. All the other pairs depend on the dealer’s upcard and on whether the table lets you double after a split.

This guide explains what doubling and splitting mean, which table rules affect them, and the full doubling and splitting decisions from basic strategy. It also includes worked examples in pounds, the most common mistakes, and how rule changes alter the house edge. If you’re completely new to the game, start with our guide to blackjack rules and basic strategy.

To double down, you add a second bet equal to your original stake. In return, you get exactly one more card and then your hand is finished. You can’t hit again, however low your total is.

A winning doubled hand pays even money on the full stake. If you bet £10 and double, you have £20 riding on the hand. A win returns £40 (£20 profit), and a loss costs £20. A push returns your £20.

Some tables also allow double for less, where you add less than your original stake. You still get only one card, so if a double is worth making, it’s usually worth making for the full amount.

The doubling rules differ from table to table, so read the rules panel before you play. These are the variations you’ll see most often:

• Double on any two cards: the most flexible rule. You can double any starting hand, including soft hands.
• Double on 9, 10 or 11 only: sometimes called the Reno rule. You lose all your soft doubles.
• Double on 10 or 11 only: common in European-style games, and the most restrictive of the three.
• Double after split (DAS): whether you can double a hand that came from a split. This changes several splitting decisions.
• No hole card: in European-style games the dealer doesn’t check for blackjack before you act. If the dealer then makes blackjack, you can lose your extra doubled or split stakes as well as your original bet.

You can only double on your first two cards (or the first two cards of a split hand). Once you’ve hit, the option to double is gone.

A hard hand has no ace, or has an ace that can only count as 1. The doubling decisions below come from basic strategy for 4–8 decks with the dealer standing on soft 17:

These hands are good to double because 16 of the 52 cards in each deck count as 10. A 9, 10 or 11 has a good chance of becoming 19, 20 or 21 with one card, and a dealer showing 2 to 6 is more likely to bust. If the dealer hits soft 17, double 11 against an ace too.

A soft hand contains an ace counted as 11, so one extra card can’t bust you. Where the table allows doubling on any two cards, you should double these soft hands:

• A,2 and A,3 (soft 13–14): double against a dealer 5 or 6.
• A,4 and A,5 (soft 15–16): double against a dealer 4, 5 or 6.
• A,6 and A,7 (soft 17–18): double against a dealer 3, 4, 5 or 6.

If doubling isn’t allowed, hit soft 13–17 and stand on soft 18. Many players are reluctant to double A,7 because 18 already looks good. Against a dealer 3 to 6, though, doubling A,7 makes more money in the long run than standing.

To split, you separate a starting pair into two hands and place a second bet, equal to your first, on the new hand. Each hand then gets a second card and is played and settled on its own. One hand can win while the other loses.

When can you split in blackjack? Only when your first two cards have the same value. Most tables let you split any two 10-value cards, such as a king and a jack, but some require matching ranks. The other rules worth checking are:

• Resplitting: often allowed up to three or four hands in total.
• Split aces: usually get one card each and nothing more. Some games allow resplitting aces. Hitting split aces is rare.
• 21 after a split: an ace and a 10 after splitting counts as 21, not blackjack. It pays even money, not 3:2.
• Surrender is not available after a split.

Here is when to split in blackjack, based on the same 4–8 deck, dealer-stands-on-soft-17 strategy. The middle column assumes you can double after a split. The last column shows what changes if you can’t.

A few of these look odd at first. A pair of 8s makes 16, the worst total you can hold, but starting two hands on 8 loses less in the long run, even against a 10. Two 9s against a dealer 7 should stand, because 18 already beats the dealer’s most likely total of 17. A pair of 5s is a hard 10, which is a doubling hand, so splitting it wastes a good start.

All examples use a £10 starting bet.

1. Hard 11 against a dealer 6. You double, so £20 is at stake. You draw a 9 for 20, and the dealer busts. Profit: £20, twice what you’d win by just hitting.
2. Hard 10 against a dealer 10. Don’t double. Hit and play the hand with £10 at risk, because the dealer’s strong card makes the extra stake a poor bet.
3. A pair of 8s against a dealer 10. You split, so two £10 hands make £20 in total. If one hand wins and the other loses, you break even. If both lose, you’re down £20. You’ve risked more money, but over the long run splitting loses less than playing 16.
4. Split 8s, then a 3 against a dealer 6, with DAS. The first split hand becomes 11. You double it, so you now have £30 in play: £20 on that hand and £10 on the other. If both hands win, your profit is £30.
5. Split aces. You get a king on one ace. That hand is 21, not blackjack, so it pays £10 rather than £15.

Remember that doubling and splitting put more money at risk on a single round. Your bankroll needs to cover those extra stakes.

• Doubling 11 against an ace in games where the dealer stands on soft 17. Basic strategy says hit.
• Splitting 10s because the dealer shows a 5 or 6. Twenty is already a winning hand most of the time.
• Splitting 5s instead of doubling them as hard 10.
• Not splitting 8s against a 9, 10 or ace because it feels like throwing good money after bad.
• Skipping soft doubles such as A,7 against a dealer 3 to 6.
• Using a DAS chart at a no-DAS table. The 2s, 3s, 4s and 6s decisions change.
• Ignoring no-hole-card rules. If extra stakes are lost to a dealer blackjack, doubling and splitting against a 10 or ace becomes more costly.

Small rule differences add up. The figures below show how each rule changes the house edge compared with an 8-deck game where the dealer stands on soft 17 and you can double on any two cards and double after a split:

A 6:5 payout costs you far more than any doubling restriction, so check it first. Our guide to choosing an online blackjack table explains how to compare rules. The same checks apply to live dealer blackjack. Most bonus terms count blackjack at a reduced rate towards wagering, if at all, so read our casino bonus terms guide before playing with bonus funds.

• Double hard 11 against 2–10, hard 10 against 2–9, and hard 9 against 3–6.
• Double soft hands against weak dealer cards (mostly 4–6) when the rules allow it.
• Always split aces and 8s. Never split 5s or 10s.
• Check the DAS, doubling-restriction and hole-card rules before you sit down.

Basic strategy lowers the house edge, but it doesn’t remove it. Over time the casino still has the advantage, and doubling and splitting increase the swings in your balance. Set a budget, treat losses as the cost of entertainment, and stop if gambling stops being fun. Blackjack is for players aged 18+ only. You’ll find more strategy articles in our blackjack guides section and other table games on our casino games page.