Understanding THAC0

For those kids who never understood THAC0…

Now you know.


Are you trying to get banned?


THACO is so confusing -I much prefer to use a chart…



Never got the Can’t work out Thac0 thing, I learnt it on my first session.

Thac0 went down at a set rate, whereas Saving Throws in 2e were all over the place :stuck_out_tongue:


Yeah. I was confused as a kid why THAC0 was a count down, but it was never hard, just weird.

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I found it complicated as a 10 year old and use it so infrequently now I find it easier to refer to chart.

It’s a bit of nostalgia though and I seldom ‘cheat’ and use ascending AC unless the game was designed that way from the begining.

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Oh good grief. Ya pansies. Roll your die and subtract it from your THAC0. That’s the lowest AC you hit.

THAC0 19 - roll of 12, you hit anything 7 or higher.

Easy peasy.

Now explain to me how AC is calculated correctly in 5e in as few words!! :smiley:


:rofl: @joe. That video is painful.

@rayotus - Yeah, I’m not sure what was going on in the background. Its like the guys was doing it stealthily before the assassins could find him.


Never had a problem with THAC0 myself. It was a convenient shorthand for pluses and minuses.


THAC0 is easy. It’s figuring CR in 5e that challenges my mathematical cockles. CR is the common core of the RPG mechanics. :man_shrugging::joy:

Try reading this shit (link below). Someone posted it in response to Peter Adkinson asking on FB if/where in the PHB it says base AC is 10. It’s hilarious. Ultimately is grokable, but it shows that some of the systems in 5e are anything but simple. There is no simple answer to what’s my 5e character’s AC?


If only TSR had explained it that way. The 2e PHB said to subtract the target’s AC from THAC0 and compare that to the d20 roll. Oh, and instead of modifying the die roll, strength and weapon bonuses modified THAC0, so you have to subtract those too.

I always just keep a note with the characters THAC0s (among other things), and when a player makes an attack roll, they tell me what they got with the modifiers they know about, and I add the target’s AC to see if they beat their THAC0. That way the target number is always the same, and AC is just another modifier.


We used to do something similar. The player added in all the mods they knew about and rolled. They then would say “I hit AC 6”, for example. Then the DM would adjudicate from that point.

I see that you are using English, which I think I’m pretty good at. But I still don’t understand what you wrote.

Simple subtraction, people! (This is the mantra and the topic that will get me banned.)

(Edit: perhaps I should amend “simple,” which is subjective, to “basic” subtraction.)