Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Categories

New to the forums? Well met! Please read the following rules of conduct for the forums, and we hope you enjoy your stay. Until swords part, friend!

+/- to THAC0. AD&D confusion.

theJoshFrosttheJoshFrost Posts: 171Member
edited September 2012 in Archive (General Discussion)
So, I've beaten the Baldur's Gate series, how ever, I went the entire saga having essentially no idea about what the base rules of the game were. For some reason, I never got a manual with the game, so really the only thing I knew about the game was that low AC was good. I had NO idea what THAC0 was, but I assumed it was sort of important.

Alright so let's see if I got this right, if you have a THAC0 if 16, and your were fighting someone with 6 AC, you'd need a 10 or lower to hit them, right? Or is it higher? I STILL DON'T KNOW.

Alright but that's beside the point. If a magic item gives you a +2 to THAC0, given the systems reliance on LOW numbers, that seems like a bad thing, right? I want my THAC0 to be lower, and if I get a +2 to my 16 THAC0, I'd have 18, and I don't want that! Do I?

Unless what they REALLY mean by +2 is it would make my THAC0 14 instead, and a -2 would give me 18. So... wat?

Comments

  • GoodSteveGoodSteve Posts: 528Member, IWD:EE Beta
    edited September 2012
    Thac0 stands for "To Hit Armor Class 0". If you have a Thac0 of 10 that means to hit someone with an AC of 0 you need to roll a 10. Everything else works on a plus/minus basis. So in the above example to hit someone with AC 1 you only need a 9 whereas if they had an AC -1 you'd need to roll an 11.

    Items that add a + to Thac0 actually lower it. So A sword that adds +2 Thac0 actually would make your Thac0 score 2 points lower than it was (ie Thac0 10 becomes Thac0 8).

    The whole lower is better but abilities that add a +1 to something actually lower it is indeed quite confusing. I'm guessing it is one of many reasons Thac0 was done away with in later iterations of DnD.
    Post edited by GoodSteve on
    GrandeCTalvraeBrudepaulsifer42
  • theJoshFrosttheJoshFrost Posts: 171Member
    GoodSteve said:

    Thac0 stands for "To Hit Armor Class 0". If you have a Thac0 of 10 that means to hit someone with an AC of 0 you need to roll a 10. Everything else works on a plus/minus basis. So in the above example to hit someone with AC 1 you only need a 9 whereas if they had an AC -1 you'd need to roll an 11.

    Items that add a + to Thac0 actually lower it. So A sword that adds +2 Thac0 actually would make your Thac0 score 2 points lower than it was (ie Thac0 10 becomes Thac0 8).

    The whole lower is better but abilities that add a +1 to something actually lower it is indeed quite confusing. I'm guessing it is one of many reasons Thac0 was done away with in later iterations of DnD.

    So, in your example, if you have a THAC0 of 10, verse a guy with 1 AC, you'd need a 9 to hit, right? So does that mean if I roll an 8, I'd still hit, or a 10 and I'd still hit?
  • ShinShin Posts: 2,201Member, BG:EE Beta
    edited September 2012
    Aye, it can be a bit confusing.

    Essentially it's like your reasoning toward the end of your post, you want your thac0 to be as low as possible, but the terminology is bonus-oriented: if you get +1 to thac0 it means your thac0 is reduced by 1, like from 15 to 14.. i.e. it just got one better.

    Likewise, if you get an AC bonus of two, it means your AC got reduced by two.. it's just more commonly called -2, whereas thac0 is not.


    In your first example, you need a 10 or higher to hit them. On a roll of 16 you hit AC 0, on 15 you hit AC 1. on 14 you hit AC 2, etc... and on 10 you hit AC 6. If you roll 9 you hit AC 7, and miss them.


    Edit: Actually let me rephrase that.. what you usually get +1 to is your hitroll, which isn't the same as your thac0. Afaik, when thac0 improves as you gain levels, the game will say that it gets reduced.
    Post edited by Shin on
  • KnettgummiKnettgummi Posts: 141Member
    GoodSteve said:

    Items that add a + to Thac0 actually lower it. So A sword that adds +2 Thac0 actually would make your Thac0 score 2 points lower than it was (ie Thac0 10 becomes Thac0 8).

    The logic behind this is that your THAC0 bonus is added to the attack "die roll" and not to your actual THAC0 score (which is the number to beat). A little inconsistent, but slightly less confusing...
    GrandeCMortianna
  • lvdisturbed1lvdisturbed1 Posts: 15Member
    You almost have it. If you have a THAC0 of 16 (reaaaaly terrible} and fighting someone with an AC of 6 you need at least 10 or better. THAC0 stands for To Hit Armor Class 0. Its the minimum roll you need to hit someone that has an AC of 0. So with your example, THAC0 of 16 vs AC of 6 equates to 16-6=10...which would be the minimum to hit. If it were vs an AC of -2 it would be 16+2.
    GrandeC
  • GoodSteveGoodSteve Posts: 528Member, IWD:EE Beta

    GoodSteve said:

    Thac0 stands for "To Hit Armor Class 0". If you have a Thac0 of 10 that means to hit someone with an AC of 0 you need to roll a 10. Everything else works on a plus/minus basis. So in the above example to hit someone with AC 1 you only need a 9 whereas if they had an AC -1 you'd need to roll an 11.

    Items that add a + to Thac0 actually lower it. So A sword that adds +2 Thac0 actually would make your Thac0 score 2 points lower than it was (ie Thac0 10 becomes Thac0 8).

    The whole lower is better but abilities that add a +1 to something actually lower it is indeed quite confusing. I'm guessing it is one of many reasons Thac0 was done away with in later iterations of DnD.

    So, in your example, if you have a THAC0 of 10, verse a guy with 1 AC, you'd need a 9 to hit, right? So does that mean if I roll an 8, I'd still hit, or a 10 and I'd still hit?
    If you have Thac0 10 that means with a 10 you will hit AC 0 and everything worse than that, ie AC 0 and higher (AC 1, AC 2, AC 3 etc) will all be hit if you roll at least a 10.
  • kilroy_was_herekilroy_was_here Posts: 455Member
    edited September 2012
    @theJoshFrost

    Let me try to break it down step by step (warning, massive wall of text incoming):

    Without any defensive bonuses, penalties or armor the A(rmor) C(lass) of any creature is 10.
    Without any offensive bonuses or penalties an attack is a straight d20 roll (1-20).
    After the attack roll, you compare it to the target's AC. In this case, anything from a 10-20 is a hit.

    Any bonus SUBTRACTS from the AC. (this is the part that makes no sense and why subsequent editions of D&D don't do things this way) Therefore a negative armor class is actually a good thing.

    aside: Typically the armor bonus is considered first, then DEX, natural bonus, deflection bonus, magic bonus etc. In D&D you are allowed ONE bonus from each type. So if you have armor on that gives you base AC6 and bracers that gave you base AC2, your AC would be 2 because only the larger of the two bonuses would apply. In this case your AC would not change even if you removed your armor, as long as you kept the bracers on.

    Basically, at the default (+)10 AC an attacker gets +10 on their roll to hit. If the AC was a very respectable -10 they would get -10 on their roll to hit you. If you were in the middle at 0 the attacker would get neither a plus nor a minus but would have to meet their threshold, their To Hit Armor Class 0 number.

    Let's go back to my first example. Without any bonuses you needed a 10 to hit someone of AC 10. If their AC was 0 you would need a 20 to hit them. (This is the weird part where it becomes easy to get lost) To 'simplify' this you would compare the number to your THACO instead so you only need to make one comparison.

    Without any bonuses, a character's THACO is 20. (You need a 10 to hit AC 10, thus a 20 to hit AC 0) Every attack bonus lowers your THACO. High STR, class levels (esp fighter and similar types), magic spells or magic weapons all make it easier to hit your target, resulting in a THACO less than 20. (Being cursed, having a very low STR etc will increase the THACO). As the game goes on, any non-magic user should end up with a negative THACO. This means that if a target has an armor class of 0 it is impossible to miss them except on a roll of 1 (which always misses).

    To use your example, if you had a THACO of 16 you would need a 16 to hit AC 0. If the target had AC 6, that would be a bonus to your result, so the number you would need to roll would be 10, a 55% chance (you need a 16 to hit 0, but his 6 AC means you need 6 less than that to hit, so 16-6=10). If his AC was -6 instead it would be (16+6=22). You can't roll 22 on a d20, but a roll of 20 automatically hits, so you have a 5% chance.

    Since you are using a d20 to hit, you can simplify things by thinking of it this way. Any bonus to your AC means that there is an additional 5% chance per point of AC that any attack will miss you. Any bonus to your THACO means that there is an additional 5% chance per point that your attack will hit. Because of wonky AD&D rules, very negative numbers for both AC and THACO are good.
    Post edited by kilroy_was_here on
    ginger_hammer
  • GruloGrulo Posts: 109Member
    edited September 2012
    Substract your roll from your THAC0.

    Let's say you have a THAC0 of 13 and you roll a 17.

    13-17 = -4.

    So you hit anything that has an AC of -4 or worse (-3,-2,-1,...,5,7, etc.). If your target has an AC of -5, you miss. Remember: In 2ed, the lower the armor value, the better it is.

    In other words: You want your THAC0 to be really low, but your rolls should still be high.
    Post edited by Grulo on
    KolonKuAmeerHM
  • kilroy_was_herekilroy_was_here Posts: 455Member
    short version: low AC is good, negative AC is better. Low THACO is good, negative THACO is better. (and -10 is better than -5 etc)
  • bbearbbear Posts: 1,179Member
    i guess the same rule set applies to saving throw? the chromatic orb save +6 bonus lowers the opponent's save value? and the spook -6 penalty raises the opponent's save value? and do you roll a 1d20?
  • kilroy_was_herekilroy_was_here Posts: 455Member
    edited September 2012
    Yes, saving throws work the same way: lower saves are better than higher ones, and magic items may make your save go even lower. On your character sheet a save may have two numbers next to it. The first is your own natural value, the second is the value modified for your equipment. So your save vs polymorph might be 15 but if you equip a ring of protection against polymorph +3 it would make your save on the sheet go down to 15 (12). The bonus makes the number go down because, again, AD&D is dumb that way.

    However, when it says a +6 bonus for chromatic orb that actually adds to the target's roll making the save easier. A penalty means that a number is subtracted from the saving throw, making a failure more likely.

    A d20 is a die with 20 sides, numbered 1-20. There is a 5% chance of any given number in that range. Whenever someone makes an attack/tries to make a save in-game, the game generates a random number 1-20, applies bonuses/penalties and determines success or failure. There is an option under setting so that you can actually see the math in the text box every time an attack is rolled. I think it's called 'show to-hit rolls'.

    No matter what you will always have at least a 5% chance to succeed (on a 20) and a 5% chance to fail (on a 1).
    Post edited by kilroy_was_here on
    Brude
  • kilroy_was_herekilroy_was_here Posts: 455Member
    It's funny... for the longest time the only things I knew about AD&D came from the Baldurs Gate series. But a few months ago I bought the AD&D core set second hand for ten bucks, so I can actually look this stuff up now. :)
  • ScarsUnseenScarsUnseen Posts: 127Member
    Simpler explanation: A +2 sword does not modify your THAC0. It modifies the result of your roll(along with your strength bonus). So...

    THAC0: 14
    Bonus to hit from strength: +1
    Weapon: mace +2
    Opponent's AC: 5

    Required roll(unmodified): 14 (THAC0) - 5 (AC) = 9 or higher on a d20.

    Roll result: 7.

    Modified Roll result: 7 (the roll) +1 (strength) +2 (magic bonus) = 10.

    You hit.
    Brude
  • DeeDee Posts: 7,430Member, Administrator, Moderator, Developer, BG:EE Beta, IWD:EE Beta
    Ahh, Thac0. Volo will have some choice words to say about this little relic, I can assure you...

    To expand on what @ScarsUnseen said:

    Your THAC0 is the target number. any attack you roll is attempting to roll higher than this number, so a lower THAC0 is better.

    Your opponent's AC is added to your attack roll to determine a hit or a miss. You also get bonuses from magic weapons, high strength scores, or certain spells or abilities.

    When you get a bonus to-hit, it's modifying the attack roll, not your base THAC0. However, it's simpler from a video game UI perspective to just roll that bonus into the THAC0, which is why it's represented as a subtraction.

    To sum up:

    THAC0: the base number that you have to beat with your modified to-hit roll in order to hit an opponent with an AC of zero.

    AC: a bonus (if positive) or penalty (if negative) to the attacker's to-hit roll.

    Example:
    Jeff Jeffrigarley has a THAC0 of 20, a Strength of 10, and is wielding a +1 Longsword that grants him a +1 bonus to attack. He also is under the effects of a spell that grants him a +2 attack bonus, for a total to-hit bonus of +3.

    Nexlit the Xvart has an AC of 4. Any attacks made against Nexlit the Xvart will receive a +4 bonus to the to-hit roll.

    Jeff Jeffrigarley attacks Nexlit the Xvart, receiving a combined to-hit bonus of +7 (+3 from weapon and spell, +4 from Nexlit's AC). Jeff needs to roll a total of 20 (his own THAC0) or higher to hit Nexlit. Jeff rolls the dice...

    And he rolls a 14. 14 + 7 = 21, which is higher than Jeff's THAC0 of 20, which means his attack hits.
  • bbearbbear Posts: 1,179Member


    No matter what you will always have at least a 5% chance to succeed (on a 20) and a 5% chance to fail (on a 1).

    But if your saving throw is below 0, does that mean it will always miss? Or the roll of 20 overrides this effect (like a critical attack)?
  • HaHaCharadeHaHaCharade Posts: 1,117Member, BG:EE Beta, IWD:EE Beta
    edited September 2012
    I like the old school +/- system LOL. I suck at math and I got it after awhile. We used to make fun of peeps in our group that needed a THACO chart to calculate their To Hit rolls (yeah we were jackasses lol). As long as you think of the "plus" on a Ring of Protection or what have you, as adding a negative bonus to your score, then its easy.
    Post edited by HaHaCharade on
  • DjimmyDjimmy Posts: 675Member
    Rolling 0 is an automatic failure to hit and rolling 20 is a sure hit in the 3rd D&D edition ruleset. I am not sure if that is the case with Baldur's Gate.
  • neur0neur0 Posts: 83Member
    You cannot roll 0, but yes:
    1 - Critical miss (always a miss)
    20 - Critical hit (always a hit)

    This means that a charmed squirrel can kill anything that doesn't fight back and isn't immune to physical damage.
    Djimmy
  • DjimmyDjimmy Posts: 675Member
    neur0 said:

    You cannot roll 0, but yes:
    1 - Critical miss (always a miss)
    20 - Critical hit (always a hit)

    lol, you can't roll 0 indeed.
    neur0 said:


    This means that a charmed squirrel can kill anything that doesn't fight back and isn't immune to physical damage.

    ...and that doesn't have damage reduction or is immune to normal weapons or something.

  • kilroy_was_herekilroy_was_here Posts: 455Member
    There was a Knights of the Dinner Table story about a deadly squirrel, but I can't find it online to share with you...

    Long story short it got mad and ran inside the warriors helm to attack his face.

    Fear the squirrel!
  • KhyronKhyron Posts: 238Member
    Wow.. lots of texts and numbers here..

    Basically, Baldur's Gate will tell you two things about your Thac0.

    Your BASE thac0 and your ACTUAL thac0.

    BASE is your unmodified Thac0, determined ONLY by level of your char.

    The number below, your ACTUAL thac0, takes into concideration your strength/dex (depending on melee or ranged weapon), your skill with said weapon and the enchantment of the weapon.

    So your BASE Thac0 may well be 15.
    Where as with the Skill, Str/Dex bonus and enchantment of the weapon could bring the ACTUAL thac0 to let's say.. 9, for example.

    Which means that the number 15, your BASE thac0, means bugger all in combat. It's your ACTUAL thac0, that will determine your chance to hit + the 1D20 you always roll.

    ACTUAL Thac0 9 + a roll of 10, means you hit ANYTHING with -1 AC or worse, but nothing with -2 or better. (Keep in mind, even if you HIT, the enemy may be immune to your weapon in which case Minsc is -usually- right. "No Effect!? I need bigger sword..")

    I hope that was simpler and easier to understand.
  • LadyRhianLadyRhian Posts: 7,057Member, Moderator, BG:EE Beta, IWD:EE Beta
    @kilroy_was_here Reminds me of the bug and the Knight from Snarfquest!
  • Roller12Roller12 Posts: 386Member
    edited October 2012
    Thac0-AC= number needed to roll to hit target.

    Can only roll 1-20, so if the number is outside that range, cant hit(or miss) (unless its a 1 or 20)


    Example: Bear has AC1, we have thac0 7

    Need to roll (7-1=6) anything from 6 to 20 to hit that bear.
    Post edited by Roller12 on
  • RomulanPaladinRomulanPaladin Posts: 188Member
    Bah! This doesn't need to be complicated!

    Here it is: HOW ATTACK ROLLS WORK IN 2 SIMPLE LINES

    1.) Your THAC0 is the number you need to roll or higher on a 20 sided die.
    2.) The opponent's AC is the bonus you get to your roll.

    Say you attack an AC 4 with a THAC0 of 15. This means that you need to roll a 15 or higher to hit. You get a +4 to your roll. Thus, a roll of 11 actually hits (11 + 4 = 15 --> 15 or higher: HIT).

    A negative AC is a "negative bonus" or, simply, a penalty. Say you attack an AC -1 with a THAC0 of 15. This means that you need to roll a 15 or higher to hit. You get a -1 to your roll. Thus, a roll of 11 misses (11 -1 = 10 --> lower then 15: MISS).

    That's it people.
  • sandmanCCLsandmanCCL Posts: 1,389Member
    This thread = proof Thac0 was a stupid system.
  • BrudeBrude Posts: 560Member
    It might have been, but I will always love it.

    Why? Mostly because when somebody asks "What's thac0?" you can loudly proclaim, in your best nasal voice, "To Hit Armor Class Zero, of course."

    As if that explanation alone is meaningful and makes sense. =P
    sandmanCCLKhamill
  • KhamillKhamill Posts: 226Member
    You can always reply thac0Bell, what...ya never heard?:/
Sign In or Register to comment.