Nearly all the blackjack tables I’ve played at in the last couple of decades have permitted double downs after splitting pairs. I used to encounter no double after split rules in single- and double-deck games, but these are mostly unplayable now because of 6-5 payoffs on blackjacks.

Blackjack rules have been tightening, but it came as a surprise when I was playing in April at a six-deck table and another player tried to double on 8-3 after splitting 8s.

The dealer was sympathetic. “Sorry ma’am, you can’t double after splits here.”

There was grumbling all around, but nobody left the table.

The rule adds about 0.14 percent to the house edge, and that assumes you make the necessary adjustments to basic strategy.

In a common six-deck game, the hands affected are 2-2 vs. a dealer’s 2 or 3; 3-3 vs. 2 or 3; and 4-4 vs. 5 or 6.

Let’s look at the numbers, assuming a six-deck game in which the dealer hits soft 17.

2-2 vs. 2: Assuming you can double after splits, splitting a pair of 2s against a dealer 2 is a defensive maneuver. If you hit, you lose an average of 11.3 cents per dollar wagered. If you split, you win enough hands and doubles to reduce losses to 7.8 cents per dollar of your original wager.

If double after split isn’t permitted, the average loss on splitting the pair rises to 15.4 cents per dollar of your original wager. You increase losses from the 11.3 cents for hitting, so you just hit.

2-2 vs. 3: The situation is similar as 2-2 vs. 2. When doubles after splits are allowed, splitting the pair reduces losses to 0.7 cents per dollar of your original wager, compared to 8 cents if you hit.

When that doubling option isn’t offered, the average loss is still 8 cents if you hit, but climbs to 9.7 cents of you split.

3-3 vs. 2: Average losses are a little higher here, but the situation is basically the same. If you can double after splitting, the average loss when splitting the pair is 12.9 cents per dollar of your original wager. If you hit the average loss is a tad higher at 13.9 cents.

With no double after splits, your average loss is 20.6 cents if you split, so you’re better off with 13.9 cents while hitting.

3-3 vs. 3: Hit, and your average loss is 10.6 cents. Split, and it’s 4.6 cents if you can double after splits and 13.6 if you can’t. So the play is to split if you can double afterward, and hit if you can’t.

4-4 vs. 5: You’d never split 4s in a “no double after splits” game, but doubling makes a difference vs. 5 or 6. It makes a winning hand even better

When the dealer has a 5 up, hitting brings an average win of 8.3 cents per dollar wagered. Split, and that win rises to 11.5 cents per dollar of your original wager if you can double after splits. If you can’t, splitting turns the hand into a small loser of 1.6 cents per dollar.

4-4 vs. 6: Hit, and your average win is 11.3 cents per dollar. Split, and that soars to 20.8 cents if you can double, but drops to 5.7 cents if you can’t.

Whether you’re trying to lose less, as with 2-2 or 3-3 vs. 2 or 3, or win more, as with 4-4 vs. 5 or 6., doubling after splits makes a difference as long as you have the correct strategy for the rule in play.