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D&D 5E Definitions, please! What are Bounded Accuracy and RAW?

Charlaquin

Goblin Queen
I've searched the 3 core books and I cant find one mention of Bounded Accuracy. Where is it, or is it just implied?
I think it's come up in blogs or interview wherein the designers have talked about the math behind the game. Couldn't point you to specifics, though.
It was one of the major selling points of the edition during the open playtest process. One of the major complaints against both 3e and 4e was the “bonus treadmill,” where level-appropriate challenges increased in DC and AC at exactly the same rate that PCs bonuses increased, making it so that if you fell behind in terms of expected bonus progression, you were at a significant disadvantage. Furthermore, lower-level threats rapidly became completely non-threatening because they literally could not hit you and you could not miss them.

To address this, WotC proposed the idea of “bounded accuracy” in the new edition, which was really more like bounded target numbers. The idea being that difficulty of DCs and ACs would no longer scale based on the PC’s level. 10 is always easy, 15 is always moderate, 20 is always hard, etc. no matter what level you are. PCs would still gain bonus as they leveled up, but they would come much more slowly, so that your bonus never outstripped the d20. While a high-level character might have a bit of an easier time hitting a certain target number than a low-level character, the difference would be relatively small, and you would never reach the point where you couldn’t miss, or an opponent couldn’t hit you.

The primary intended effect of this change was to make it so that low-level monsters could remain a threat to high-level characters in enough numbers. In 3e, it doesn’t matter how many Kobolds you throw at a 15th level party. They just can’t hit the PCs, so they are not a threat. In 4e, they tried to address this by having different stats for different kobolds - so while standard Kobolds wouldn’t be able to hit a 15th-level PC, a special elite kobold soldier or whatever could. This was very unpopular with a certain crowd, so with 5e they decided to instead flatten the math. Now, one kobold may not be a threat to a 15th level party, but enough of them will be. This benefit also goes the other way - 5e characters can punch above their weight class by using numbers and clever tactics to their advantage, which 3e and 4e characters couldn’t because of how the math worked.

Finally, bounded accuracy was supposed to make it so that magic items with +X bonuses to hit or AC would be genuine bonuses. You wouldn’t “need” a weapon with a certain bonus by a certain level to keep up with the treadmill. In fact, magic bonuses would always put you ahead of the mathematical expectation. So those bonuses would feel like true bonuses, making things actually easier instead of keeping them from getting harder.

You don’t really hear about Bounded Accuracy much any more except from people who played a lot of 3e and/or 4e and participated in the 5e open playtest, because the concept isn’t really meaningful except in contrast to the math of those editions. The articles and blog posts on the subject have long been taken down, and I doubt WotC has much interest in talking about that stuff any more. The goal at the time was very much to win over people who disliked 4e. But these days, 5e doesn’t need to sell itself on being “not 4e,” so a lot of the design choices that specifically addressed common 4e grievances just don’t get talked about any more because they don’t need to be.
 

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prabe

Aspiring Lurker (He/Him)
Supporter
@Charlaquin Thanks for the summary. I wasn't playing D&D during the playtest--I might not even have been playing TRPGs--so I missed all the discussion when it was current.
 


fearsomepirate

Adventurer
Here's how I think of it:

d20 + modifier is a dead simple RNG to use. It's fairly easy for players to intuit, "I have a +10, so I have to roll a 6 or better...I have a pretty good chance of this." A quick player might even notice that he has an exactly 75% chance of success. The price of this ease of use is it's just plain bad at handling extremes. All you can do with d20 is shift it up or down 5%. It's not very granular, and does a bad job of representing anything where the variance is in the tail of the bell curve.

So what do you do? 3.5's approach is to basically ignore the problem and try to represent extreme-scale probabilities with gigantic modifiers, which results in a system that is ultimately impossible to intuit and results in useless skills. 5e's approach is more to just accept the limitations of the d20 system. This results in some silliness, like an overly compressed gap between "novice" and "master" on the skill chart, but the answer is just, "Well, that's just a limit of the d20 system."
 

Charlaquin

Goblin Queen
Here's how I think of it:

d20 + modifier is a dead simple RNG to use. It's fairly easy for players to intuit, "I have a +10, so I have to roll a 6 or better...I have a pretty good chance of this." A quick player might even notice that he has an exactly 75% chance of success. The price of this ease of use is it's just plain bad at handling extremes. All you can do with d20 is shift it up or down 5%. It's not very granular, and does a bad job of representing anything where the variance is in the tail of the bell curve.

So what do you do? 3.5's approach is to basically ignore the problem and try to represent extreme-scale probabilities with gigantic modifiers, which results in a system that is ultimately impossible to intuit and results in useless skills. 5e's approach is more to just accept the limitations of the d20 system. This results in some silliness, like an overly compressed gap between "novice" and "master" on the skill chart, but the answer is just, "Well, that's just a limit of the d20 system."
5e also empowers the DM to cover the extremes where the dice mechanic breaks down. That’s why 5e recommends calling for a roll only when, in the DM’s assessment, there is a reasonable chance of success, reasonable chance of failure, and appropriate stakes (i.e. a meaningful consequence for failure).
 
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We use the RAW AC rules. I don't typical give magical armor (at least not with AC bonuses) and we don't multiclass (5e default). Our group (lvl 15) is 2 fighters, a thief, a ranger (scout), and a wizard. No one typically has an AC above 20 (plate + shield).

I'm sure it is easy to allow high AC if you want, but it is trivially easy to keep it limited by RAW.

Even under those rules (no MCing, no magic armor, PHB only) an EK Fighter is easily hitting AC 26 (with shield, and no other buffs) from 3rd level onwards.
 


fearsomepirate

Adventurer
Even under those rules (no MCing, no magic armor, PHB only) an EK Fighter is easily hitting AC 26 (with shield, and no other buffs) from 3rd level onwards.

Shield is a reaction spell that lasts a single round, and an EK can only cast it a few times per day. If your DM hits you with 6-8 encounters, you aren't even able to use every encounter until fairly high level, let alone every round. These kinds of temporary, contextual buffs aren't really what anyone means by a character's AC.
 

dave2008

Legend
Even under those rules (no MCing, no magic armor, PHB only) an EK Fighter is easily hitting AC 26 (with shield, and no other buffs) from 3rd level onwards.
That could be true, but again I originally stipulated no magic. Shield is magic, and in our case we don't have a EK. Also, shield requires a resource and a reaction, so that seems a fair trade IMO. Finally, it still isn't easy to get AC 26 in my games. Plate armor is not a thing that just grows on trees. Even chainmail is really a bit much for most adventurers. Unless your lucky, an adventurer is unlikely to get anything better than studded leather until at least level 5 and I don't think anyone got heavy armor until after 10th level.

Listen I know it is easy to get high ACs, it is also easy to not give those out. That is all I'm saying.
 


auburn2

Adventurer
Even under those rules (no MCing, no magic armor, PHB only) an EK Fighter is easily hitting AC 26 (with shield, and no other buffs) from 3rd level onwards.
I disagree with this for three reasons. First barring feats or another multiclass he is hitting 26AC for exactly 2 rounds a day, factoring misses against AC21 it is probably the equivalent of 5-10 rounds but hardly all the time. Second, without magic you need to take defense fighting style, meaning it is impossible unless you do this. Finally I don't think many 3rd level characters have plate. I know the two games I am playing right now with 3rd level characters, one has about 27gp and the other has about 60gp. Now they do have a few gems I don't know the value of and they have bought some things but not nearly enough to finance plate armor even if they had scrounged, avoided buying better weapons, decent food and adventuring gear and saved just for plate.

The only character I have played or seen played that managed 26 AC by third level is a bladesinger in bladesong, and that was with great ability rolls and a staff of defense.
 
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