What happens if I set up for a "29 hand" and miss?
Indeed, playing for 29 can be a very risky proposition - especially if you're in a late stage of the game and stand a good chance of losing if your hand scores no more than 14.

To simplify, I'm setting aside any human influence here. Yes, there are two other cards known to the player, as well as six cards known and controlled by the opponent. However, none of these are going back into the deck and no further cards are being drawn.

At best, a player might be able to use the two other cards in his hand to adjust his expectations of what the up-card could be. Of course, there's no chance at nailing 29 if you have all four 5s dealt to you along with a J and something else. But if your extra two cards each have a face value of 9 or lower, the odds that the up-card will substantially improve your score just went up a notch.

Still, setting aside all factors except the 4 mandatory cards in the starter hand simplifies calculations and gives a relatively solid baseline for our expectations.

Once you take out the rainbow hand of three 5s and a J, you have 48 cards left in the deck. Of these, the possible up-card scenarios are:


The 5 that matches the in-hand J (29 points, 2%) - This is the only way to score 29 and maximize this hand. And there's only one card that can do it.
Any remaining J (22 points, 6.25%) - This adds three more 15s and a pair to your base, for an 8-point boost. Counting out just the given base hand, there's three of these left in the deck.
T/Q/K matching the in-hand J (21 points, 6.25%) - Again, giving you three more 15s. Add on the knob and it's a 7-point total boost. Also, like the Jacks, there's only three ways to do this.
Any other T/Q/K (20 points, 18.75%) - Not matching the in-hand J, but still having face value of 10, means we lose the knob/pair points but keep the 15s. There's nine ways to do this though, so our odds here are relatively favorable in comparison to the previous scenarios.  


Totaling the above gives us a one-in-three chance of scoring 20 or better. With a minimum possible score of 14, that's still a very nice hand! 

However, as you'll see below, two-thirds of the possible scenarios will only bump your score by one point at most - and the majority of those don't add to it at all. If scoring 16 or more is absolutely crucial in the round where you get this hand, you might want to put off your dreams of hitting 29 for another day.


Any other card matching the in-hand J (15 points, 16.67%) - Anything other than 5/T/Q/K, which matches the in-hand J, only gives us one additional point for knobs. No extra 15s or pairs. This is where things start looking relatively bleak, since there's eight ways to do it.
Any card not categorized above (14 points, 50.00%) - This is the bare-minimum possible score with a hand that might otherwise score 29. We've got the three 15s for pairing each 5 with the J (6), the one 15 by adding all the 5s (+2), and a three-card match between the 5s (+6). Any up-card that's not a T/J/Q/K, and doesn't match the in-hand J, will not add to this. Having 24 ways to do this, out of 48 possible up-cards, gives us coin-flip odds of being stuck with the minimum score for this hand.