Attack rolls and 50% miss chances

[Tinalles]

Suppose your PC is blinded, lacks the blind-fight feat, and wants to smack something. Doing so requires an attack roll, and suffers a 50% miss chance.

In order to do this, I often see people use this procedure:

1) Make the attack roll.
2) Do all the math to determine the attack value.
3) Roll percentile dice to see if it was a miss.

This is slow and cumbersome. So at my table, I encourage to people to do this instead:

1) Roll your d20.
2) If it's an odd number, you miss.
3) If it's an even number, then you add up your attack bonus.

I find this much faster. It only requires one die roll per attack, not two, and you know immediately whether or not you've passed your miss chance. Knowing that prevents you from wasting time on math that isn't necessary. And it integrates seamlessly with the standard rules for automatic miss (natural 1, odd) and automatic hit (natural 20, even).

Just thought I'd put that out there. I hope someone finds it useful.

[Quantum Steve]

Well, it changes the probability of a success, but only a bit, so I guess it's an OK variant.

[Matthew Downie]

Worst-case example of how it alters probabilities: you have an attack roll of +10. They have an AC of 28 and are invisible. Under the normal rules, you have a 15% chance hitting (18, 19 or 20), followed by a 50% miss chance, for an ultimate hit chance of 7.5%.

Under these rules, an 18 or a 20 hits, which works out at 10%.

Another possible method:

Roll a d20 and a d6 at the same time. If the d6 is 1-3, you miss. Otherwise, calculate your attack roll as normal.

[Zhayne]

I agree with Matthew Downie. Just throw the concealment-check-dice at the same time you throw the attack die.

[Tinalles]

Matthew's approach is also a good way to do it.

I hadn't crunched the numbers to work out exact probabilities, so that's interesting. It looks like the overall change is pretty small -- 3.5% in Matthew's example -- which strikes me as acceptable for the convenience.

[ryric]

Your way also means that a miss chance will never negate a crit, which is a symptom of your system being a bit more swingy. Players will be happy when their PCs' crits aren't negated, but unhappy when their major cloak of displacement has no chance to save them from a nat 20.

It also doesn't really work with 20% miss chances.

[blahpers]

I don't find flipping a coin to be much of a slowdown. If it helps, you can roll the miss chance before the attack roll--that way you don't have to worry about tears all over your game mat when the scythe-barbarian critically hits the air. : )

[SorrySleeping]

I think the problem comes with the d100. There is no reason to roll a d% when your odds are 50/50.

Rolling multiple dice is the solution, if you really want to speed up play.

[Claxon]

Yeah, I've always rolled miss chance first or rolled them together.

There no reason to use d% for 50% miss chance. Just use a d6 with 1-3 being miss and 4-6 being hit. You could also use just a d10. Is needlessly complicated unless you really have so many possible outcomes they can't fit on any smaller die.

[maouse]

My approach is: Declare the attack. Roll a percentile. If it is under 50% don't bother rolling an attack. You missed.

You can do the even / odd die roll if you want. Or even toss a coin. But who doesn't like rolling 10 siders. They are fun and pointy!

(move step 3 to step 1... reduces rolls needed 50% of the time)

[KahnyaGnorc]

There is no reason to use d% for 50% miss chance, except that it is fun to roll d% . . . Ok, I know I'm weird.