Discount Gambling

I recently saw the Instant-18 blackjack side bet, and I thought it was funny. It’s an even-money side bet that plays against the dealer as a hand of value 18. Hence, the name “Instant-18”. You put up a bet, and it’s an 18. It has a 2.036% house edge for a 6-deck shoe, but it’s still kind of interesting. It’s an optional side bet where (typically) you can bet an amount less than or equal to your main blackjack bet. Of course, I had to see if this bet was countable.

First, I looked at the distribution of EVs after 5 of 6 decks were dealt from the shoe:

This looked promising, so I checked out the EORs for the bet:

From the EORs, I made a simple count system, where Aces are +3, Sevens are -2, and Deuces are -1. Then I plotted the EVs of the main and side bet vs. the true count:

Unfortunately, when the count for the side bet gets good (true count >= 4), the main bet is -EV. However, for a good enough count (true count >= 7), the combination of (main bet + side bet) is +EV. Also, for a bad enough count (true count <= -3), them main bet is +EV.

So, by itself, the Instant-18 side bet gets good (true count >= 4) about 7.8% of the time, with an average return of +1.53%.

Of course, you can’t just bet the side bet when it gets good. You have to have a main bet to bet the side bet. If you bet both when the combination gets good (true count >= 7), or just the main bet for true count <= -3, and Wong all others, you'll bet 13.9% of the time with an average EV of +0.47%.

As usual, these things are interesting, but not practical.