Ascending v. Descending Armor Class

Nothing I've seen has provoked so much controversy within the old school community as ascending versus descending armor class. Labyrinth Lord, like B/X, uses a combat matrix with to hit rolls against descending armor class. Basic Fantasy RPG and DCC RPG, like 3.5, use an attack bonus versus 10+ ascending armor class. Swords & Wizardry splits the difference. What does ACKS use? Well, neither. With ACKS, we started by acknowledging that all the player really cares about is  "what number do I need to roll to hit".  We wanted to find the absolutely easiest way possible to deliver that information. It turns out the system we needed was there all along, in the form of B/X saving throws. Everybody immediately grasps how old school saving throws work. If you have a Saving Throw versus Poison of 14, that means you'll need to roll a 14+ or succumb to the poison! It's clear just from looking at the character sheet what the player has to roll on the d20 to succeed. Following this logic, in ACKS, each character gets an "attack throw" value - this is the number he needs to roll to be successful at attacking ( just like a "saving throw" value is the number needed to roll to be successful at saving.) A normal man's attack throw is 11+, meaning he needs to roll an 11+ on 1d20 to hit. Armor makes a target harder to hit. The target’s Armor Class is added to the attack throw value necessary to hit it. A target with zero armor has, intuitively, an armor class of zero. A target with leather armor has an AC 2, while one with platemail and shield has an AC of 7. If your attack throw is 11+, and your target's AC is 2, you will hit the target on a roll of 13+. Converting to the ACKS "attack throw" system is easy, and once you use it, we think you'll find it the most intuitive to hit/armor class system yet.  To convert --
  • From B/X: ACKS AC = 9-AC; ACKS Attack Throw = THAC0-9
  • From 3.5: ACKS AC = AC-10; ACKS Attack Throw = 11 - Base Attack Bonus


Nice idea. I like it. and to convert from Dragons at Dawn or Spellcraft and Swordplay, you just subtract 1.


I haven't played either of those games, though I've read Spellcraft and Swordplay... Not familiar with Dragons at Dawn at all.

Heh, ask Tavis. ;)



Oh, wow! Thanks, Tavis, I love it when a game system I like is taken into consideration—makes me respect whatever the process ended up with a lot more. I’ll give ACKS a big second chance for this.

Descending attack bonus, eh?
Did you know about the Target 20 idea? What do you think of it?

I was a big advocate of Target 20. It definitely informed our thinking. However having run the first Dwimmermount game using ACKS but without actually having its rules near to hand, I am a convert to the system Alex's playtesting settled on. In my experience not even Target 20 has been so easy for me to do on the fly in my head, mostly because if I know you need a 10+ to hit anything at first level half the time I just look at the dice and don't calculate. Target 20 I feel like I have to do the math even if it should be clear it's going to miss.

I bought it on DtRPG… what’s this about a coupon? Is it some page in the PDF that is the coupon? Where is it?

Oh, I see—it’s only in America?

Sorry for the slow reply! No, you can use the upgrade coupon in the PDF at any Game Salute Select store in the world that carries the ACKS hardback, or go to to use the upgrade and have the book shipped to you.

If your favorite local store isn't carrying our books, tell them you'll be a customer if they do, and have them visit to sign up!

I disagree with your assessment as to the intuitiveness of the system.

I'm a LL/Basic guy myself, but this is the one thing that 3.x got perfect. It just doesn't get any easier than the attack bonus system.

Roll 1d20, add modifiers. That's the AC you hit. There's almost zero calculation involved. If you have no modifiers and you roll a 16...guess what you just hit...AC 16 (or worse).

Your system, while completely functional, is certainly not more intuitive than 3.x and, personally, I don't find it more intuitive than an attack matrix.

I’ve kept thinking about this.
My own ACKS campaign is still vapor but I played a session in a LL-AEC campaign that they’ve houseruled to use ascending AC + BAB, i.e. 19-RAW AC. Similar to 3rd ed. (We still need the RAW AC for a few things, such as Monk's instakill percentage, but the inverted AC is what we’ve listed on our sheets.)

Combat was still fast in our group. We used group initative and when it was the player’s turn we all went crazy, rolling damage along with the d20 and shouting out things like I miss! or I hit, 5 damage—BUT that was only possible after a few rounds, once we had figured out the enemy’s AC, and, what was worse, we had to add our BAB to every roll. I guess it was a good thing that the BAB was still 0 in most cases! The joys of early levels…

So works OK. Still, I find myself wishing that we used the ACKS system, but with the caveat that you knew the opponent’s AC so you could add it to your attack throw before you even rolled the dice.

When you have to go “I hit by five”, that means you also have to subtract and almost everybody is less comfortable, even though we all can do it, with substracting on the fly than addition or, better yet, a simple comparison.

Looking at the “equations” from Delta’s post about Target 20, I think his priorities are backwards. I think the D20 should be placed alone on one side of the comparison operator.
As it is he has plenty of math that you have to do just after you roll the dice. I don’t want that, I become very impatient once the dice have settled.

Even without my caveat, I’d still prefer the ACKS way because, as Tavis says, you can tell something is a miss for sure if you roll under your attack throw, and you can figure out the AC after a few rounds.