Question about THAC0

[CJOLL4]

I haven't played D&D in a long time, which leaves me wondering about THAC0; the lower your THAC0, the better, right?

Right now, I'm looking at a CRESCENT HATCHET. One of its attributes is "THAC0: -1" which seems like it's a good thing. But the weapon's description says "...not only is it extremely heavy, but the balance is poor and the edge is dull and pitted. Despite the difficulty in using the hatchet in combat..." Which indicates to me that it would have a penalty to hit, not a bonus. Can anyone shed light on this for me? Thanks

[figmentPez]

Just one of the many frustrating parts of old school D&D. A +1 to armor class lowers your AC. A +1 to THAC0 lowers the number you have to roll to hit. Chalk it up to the idea that bonuses should be expressed in positive numbers.

It's easy enough to show that the Crescent Hatchet's -1 is a detriment to your ability to hit because magical weapons all have +1, +2, +3, etc.

[Duilf]

if i remember correctly atleast in the older versions of the rules thaco or to hit score is that you have to roll a 20 sided dice and get atleast your thaco to hit after modifires then what you are hitting rolls a armor class roll to dodge that works simulerly. it basicly works to the effect of the exact opposite of how most minds think it should therefor even when most people have a grasp of it it bugs them

[wendigo211]

Prior to 3rd Ed. D&D, in order to hit:
d20 + Hit modifiers -AC modifiers>= THAC0-AC

That is to say, your roll on a 20 sided die +any modifiers you have would have to be greater or equal to your THAC0 - the target's AC.

E.g. Say your Level 5 good Fighter with an 18:50 strength, who is specialized (2 proficiency points) in hammers attacks an Orc using a +1 Warhammer. The Orc has a 4 AC and is under the effects of a Protection from Good Spell (+2 AC vs. good creatures) A level 5 Fighter has a 16 THAC0, the Orc has a 4 AC, so THAC0-AC=12. The hit modifiers are:

• Strength bonus to hit:+2
• Specialization bonus to hit: +1
• Enhancement bonus on the weapon: +1

If we add all these modifiers together we get +4. The Orc has +2 AC modifier.
So in order to hit:
d20 + 4 (hit modifiers) -2 (AC modifiers) >= 16 (THAC0) -4 (AC)
d20 +2 >= 12
Or we can shift the modifiers to the other side of our inequality,
d20>=10
Our fighter would need to roll a 10 or higher on a D20 to hit the Orc giving him a 55% chance to hit.
Since we have that +4 modifier everytime we attack with that +1 Warhammer, we tend to say our character has an "effective THAC0" of 12 (16-modifiers), or with things like Dex bonus or a Ring of Protection we have an "effective AC" of AC-modifiers.

TLDR: modifiers get subtracted from AC or THAC0, so positive modifiers lower those numbers (good thing) and negative modifiers raise those numbers (bad thing).

[CJOLL4]

Thanks for the clarification, everybody! I never used the hatchet, but I did find a magical ring that said "Armor Class: +1." I thought "surely that's a bad thing" but then I put it on to test it, and it LOWERED my armor class. That's pretty un-intuitive