AD&D 1e Combat Tables and THAC0 explained with examples

I explain how the Advanced Dungeons & Dragons and Second edition Advanced Dungeons and Dragons combat tables and THAC0 works, and how they are essentially the same thing. In either system, once you know the THAC0 of a character, you can easily calculate the to hit number.

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[retrodmray]

THACO - Roll = AC hit. Prevents telling PC what the true AC is. 🤓But using these attack matrices prevents un-hit-able targets without using the 'Nat 20 always hits' rule. Repeating 20's fixes this all lower levels for sure! Thnx for this!

[alexandersmith]

Ah yes my favorite fast-food restaurant; Thac’o Bell! 🤣👍.

[Wendigo]

Written directly beneath Table I.B is the following:
"Special Note Regarding Fighters' Progression: This table is designed to
allow fighters to advance by 5% per level of experience attained, rather
than 10% every 2 levels, if you believe that such will be helpful in your
particular campaign. If you opt for a per level advancement in combat
ability, simply use the table but give a +1 "to hit" bonus to fighters who
attain the second level of experience shown in each group of 2 levels, i.e.
1-2, 3-4, etc. You may, of course, elect not to allow per level combat advancement"
It's a Gygaxian typo fest as he means to say the table accomodates 10% advancement per two levels but has the situation reversed. That said increasing THACO by one step per level is a valid alternative and not a house-rule you would need to make up.

[ryannilsson]

You did a really good job of explaining THAC0, and illustrating it from Monsters in the Fiend Folio was a great idea.

[ObatongoSensei]

Tables in earlier editions were actually pretty weird, since they showed some not that intuitive progressions of to hit numbers for really high or really low ACs. You can see in many cases it's not consistent with just subtracting target AC from the 0 line.

It became pretty streamlined with AD&D 2nd Edition, when thac0 was just a function of your character level and the group it's class belonged to: all started at 20 at 1st level, then the different groups dropped a specific number of points at a specific level increment.
Warriors dropped 1 per level, as you noticed, priests dropped 2 points every three levels (no fraction allowed), rogues dropped 1 point every two levels, and wizards dropped 1 point every three levels.
Later there was also a function for the psionicist group and class, which I don't remember at the moment, but it was similar to the rogue progression.

You could figure out your thac0 from the table or just calculate it yourself with ease. No need for complex tables and no weird results when hitting caps.

[doctorlolchicken]

I never see anyone say this, but the way we did it was their AC became the bonus to your d20 roll. So if you need 10 to hit AC 0 and they have AC 5 then you roll d20+5 and need to get 10 or more. I know it’s exactly the same as subtracting 5 but we found it more intuitive.

[JohnDretired]

Not being able to handle THAC0 is essentially admitting that grade 1 math had defeated you.

[BlackJar]

Thac0 shows up in the Masters Set (the black box) for "basic." Thac0 was derived from the tables as an easy way to get the numbers without looking it up, but it's actually a simplification -- for some extreme ACs it breaks down as the tables repeated numbers like 20, 25, 30, and so on (I think a predecessor to natural 20s being special).

[pgpegxp]

THACO was not used until 2nd edition. 1st edition used charts based on character class and level against AC.

[Nexusofgeek]

This was a good explanation but you kind of gloss over the fact that there was a bit more to it in second edition, you not only considered the Thaco and AC to come up with the "to hit" number, you also need to consider the modifiers which can lower or raise the to hit number quite a bit. For example, the fighter's strength and situational modifiers such as the attacker being on higher ground, rear attacks and whether the target is surprised, just to name a few. These are in chapter 9 of the PHB for 2e. Not sure if these are factored in also in 1st edition, I'd have to look at my old books.

[KabukiKid]

I'm honestly blown away that TSR employees apparently pronounced THAC0 different! lol I never heard that before. Someone needs to ask one of them for a definitive answer about that. I need to know now! lol :-)

[Stringtheorist]

I always pronounced it "Thwacko". 😂

[xaxzander]

The reason 2nd ed was not a best seller? Ya you don't need it if you have the 1st Ed. books.

[Treblaine]

I still cannot fathom why they decided a lower armour class would be "better". Why wilfully go into the negative for no reason?