D&D General Explain Bounded Accuracy to Me (As if I Was Five)

[NotAYakk]

Bounded accuracy means there is a reasonable chance to hit or miss a foe, even if they are extremely weak or strong. It means that the d20 is a large component of if you hit or miss.

In comparison to 3e and 4e where to hit and AC modifiers went into the stratosphere, ranging from +5 to +45. With that range, the d20 added means any foe one has a chance of both hitting and missing, the other doesn't bother to roll.

Bounded accuracy goes back to old D&D where at level 1 you had low accuracy, and it climbed as you got to higher levels. Your effectiveness being a product of expected accuracy an damage per hit, it allowed characters to scale without their damage scaling as fast.

Ie, an expected 25% accuracy at level 1 climbed to an expected 75% by level 9 meant the exact same weapon damage did 3x the damage per attack.

Small accumulated increases in accuracy and defence have surprising impacts on effectiveness. An otherwise identical character with +5 to accuracy and defence is close to twice as powerful as one without: in 3e and 4e this effect can dominate the game. It is a large component of why a level 20 PC in 3e was considered 700x stronger than a level 1 PC, and in 4e a level 30 PC was 150x stronger than a level 1 PC. In 5e it is closer to 20x; a CR 1 creature is a medium difficulty fight for a party of 4 PCs in 5e, and 21 of them are medium for a party of L 20 PCs. 1 CR standard encounter in 3e is 1 for level 1 party and 725 for L20 party. In 4e a level 1 solo is equivalent XP wise to a level 9 normal monster, which is roughly XP equal to a level 20 minion, and 135 L20 minions makes a medium difficulty L30 fight for 4 PCs.

Bounded Accuracy - slower growth in to hit and defence, and keeping the range over every PC level smaller than the d20 - makes that somewhat plausible and keeps the power scaling down.

More of character power moves to the size of the impact, and not if the action missed or hit entirely.

 

[DammitVictor]

Basically... all the task resolution is on the same d20. You roll a d20, you add your bonus, you try to meet or exceed the DC.

Bounded Accuracy means that the range of possible bonuses is less than 20 (-1 to +17, roughly) and the range of significant DCs is 20 points exactly (10 to 30) so any roll that your character is normally expected to attempt, the best character will always fail on a 2 and the worst character will always succeed on a 19. Most of the time, there will be less than a 10 point (50%) variance between any two characters.

Means that any two characters in the same situation are, more or less, playing the same game. They can attempt all of the same basic character actions-- weapon attack, common skills-- and have a reasonable chance of success. The range of defenses between two characters stays consistent, more or less, for all monsters and all levels. (Armor Class, at least. Saving Throws are a problem.) The DM can deploy the same monsters against every member of the party without worrying that a monster can't miss some characters and can't hit others.

Near as I can tell, 5e does this fairly decently. I think character non-class and non-spell abilities are too flat between tiers of play, but I'm really impressed by how well they got the game away from numbers go up.

 

[R_J_K75]

One thing that bothers me about bounded accuracy is that if it is such a major design philosophy of 5E D&D, as far as I remember it is not mentioned or at least briefly explained in the three 2014 core books, is it? I don't recall it being in them.

 

[billd91]

One thing that bothers me about bounded accuracy is that if it is such a major design philosophy of 5E D&D, as far as I remember it is not mentioned or at least briefly explained in the three 2014 core books, is it? I don't recall it being in them.

It's mostly an underpinning of the design philosophy of 5e in contrast to 3e/4e. Since the rules are written independently of prior editions, it probably doesn't need to be directly mentioned.
That said, more designer notes in rule books would be appreciated, if you ask me.

 

[Parmandur]

For quite a while I've seen the term bounded accuracy thrown around but I don't think I ever saw someone explain exactly what that was. Fair enough. I decided I wanted to know, so I put on my big boy pants and Googled the heck out of it. There's even an entry on the D&D Wiki. But then the wiki says BA has nothing to do with skill checks even though other people totally say it has something to do with skill checks. Not sure what that means. What I can gather is that BA has something to do with how difficult it is to hit something in combat. Is that it? Someone explain it to me as if I recently suffered a head injury. What's good about it? What are the drawbacks?

I almost called it Bonded Accuracy in the thread title.

It means that DCs and modifiers stay in a limited range on a bellcurve: no DCs or AC over 30, for instance (no published stat block actually gets up to 30 AC).

This means the lowest of tge liw always have a chance to make a roll, and the highest of the high have a chance to fail (mostly).

 

[Parmandur]

One thing that bothers me about bounded accuracy is that if it is such a major design philosophy of 5E D&D, as far as I remember it is not mentioned or at least briefly explained in the three 2014 core books, is it? I don't recall it being in them.

No, it's entirely a behind the scenes design philosophy that was discussed in Next playtests. However, the math of 5E as published embodies the principle.

 

[Reynard]

It's mostly an underpinning of the design philosophy of 5e in contrast to 3e/4e. Since the rules are written independently of prior editions, it probably doesn't need to be directly mentioned.
That said, more designer notes in rule books would be appreciated, if you ask me.

I think it is helpful when the designers talk to GMs, because, ultimately, GMs are designers too.

 

[tetrasodium]

For quite a while I've seen the term bounded accuracy thrown around but I don't think I ever saw someone explain exactly what that was. Fair enough. I decided I wanted to know, so I put on my big boy pants and Googled the heck out of it. There's even an entry on the D&D Wiki. But then the wiki says BA has nothing to do with skill checks even though other people totally say it has something to do with skill checks. Not sure what that means. What I can gather is that BA has something to do with how difficult it is to hit something in combat. Is that it? Someone explain it to me as if I recently suffered a head injury. What's good about it? What are the drawbacks?

I almost called it Bonded Accuracy in the thread title.

Ruleslawyer did a great video on its failings recently. Others have mentioned it but none linked or embedded it.


In short bounded accuracy in 5e fails at pretty much everything it promised and creates a bunch of damned if you do damned if you don't type problems for the gm to be blamed for either way

 

[Reynard]

none linked

 

[FitzTheRuke]

Yeah, they don't NEED to talk about it in the Core Books because it is not important for anyone to know about to PLAY the game. However, it's an interesting design philosophy, and SHOULD be talked about more openly, like all their design decisions.