At what point does AC stops being an issue?

[Heavenblade]

Im planning a character for a solo game - a fey wanderer ranger, with the following stat array and ACFs


Half elf
Revised ranger (Spell versatility, hunter's mark instead) 8
Fey wanderer
Feats (free feat at lvl 1)-resilient (con), stealthy (UA)

Scores
Str: 15 +1 +2 (racial+ASI) = 18
Dex: 13 +1 (feat) = 14
Con:10 +1 +1 (feat and racial) = 12
Int: 8
Wis: 14
Cha: 12 +2 (racial) = 14

Longsword, half plate

I get one uncommon magic item (mithral for my half plate to be a sneaky) and one rare (havent decided yet, probably a weapon)


The character is actually a paladin from a former game and edition who was revived after the event of said game.

Currently, with half plate, my AC stands in a respectable 17. Im cuurrently debating between sword-n-boarding it or taking a longsword/greatsword, and take the mariner combat style.


If I go for mariner Ill end up at 18, but if I take a shield I can get up to 3 more AC if I take a magical +2 shield. This raised the following question, at least for me. Obviously, there's quite a difference between 10 and 15 AC, or 13 and 18.

When does this difference stop mattering, if ever? Are these 3 points of AC gonna change something meaningful in the way the character acts, or if something could hit me on 18 it could also hit me on 21 and vice versa? (Not exactly, asking more in the general sense of things)

[Zhorn]

There's going to be a more in-depth-mathy answer by one of the smarter forum users on the ideal AC breakpoint for optimized builds at some point, but on the surface level the answer is ultimately too DM/campaign dependant.

You can end up facing primarily singular high +hit opponents that outpace your AC (beating your AC by 1 or 15 is all the same), or casters that primarily target saving throws making AC near worthless.

Or you could be facing hoards of mobs and countless minions in strings of dungeon crawls where AC is king, and the higher is the better.

For covering your bases, the high teens will serve you well in most campaigns, eventually hitting the 20's later into progressing with some magic items and/or expensive upgrades, but be sure to give some attention to the other defences.

[CTurbo]

I always like my AC to be as high as reasonable possible without min-maxing the entire character around it. I'd go half plate + shield + Defense/Mariner style for 20 AC. Ring or Cloak of Protections are pretty easy to come by too adding an additional +1.

[rlc]

The Tarrasque has +19 to hit, so I guess 39+ ac would be the real answer.

[sophontteks]

It stops mattering once a monster needs to roll a 20 to hit. Every AC after that point is useless. Prior to that point AC matters a lot, but obviously it only matters when it comes to avoiding getting hit by attacks (this is important because a good tank must consider saves as a part of their defense and AC does nothing if you arent a target.)

[Spore]

Let's just take a few enemy examples.

A mere wolf (CR 1/4) has +4 to attack.
An adult red dragon (CR 17) has +14.
A vampire spawn (CR 5) goes at +6.
Niv-Mizzet (CR 26), an ancient red dragon from Ravnica has +17.

Furthermore, for my own purposes, I assume the magical barrier of AC = 10+enemy attack bonus. to be something to aim and surpass. Why? If your enemy has +4 to attack, and you move from AC 15 to AC 16, you effectively cut his damage by 10% instead of five (you reduce his 50% chance of hitting you by 5%, and 5%/50% = 1/10 = 10%, basically doubling your AC investments).

Now, any SANE DM wouldn't let you fight a red dragon solo, and only the most deranged ones let you fight it without magical gear. So we take your AC 18, which is okay but not great reducing incoming damage by 10%. I assume your DM at least gives you a way to increase AC via shield and armor (let's be stingy, and go with a +1 armor with a special effect and a +2 shield). Suddenly your armor is 21.

But wait, there is more. You helped a cleric along your quest, and you can procure the spell Shield of Faith. Maybe your amulet can cast a Shield spell on top of that. Your AC is 23, which is tremendous, maybe you can blind it (imposing disadvantage, aka about a +5 mod to your AC) and you pop a single shield to enter the arena and prepare your blinding attempt.

Ultimatively there is so much an experienced DM can aid you in slaying an unsurmountable foe, but if your Lv 15 butt is facing a dragon without magical aid or decent items? Nope out of there. No one in character would DARE to fight such monsters without proper preparations. Not even a 17th level ranger.

[stoutstien]

Another thing to add to this is at a certain point getting a good source of disadvantage on incoming attacks is going to outweigh the cost of additional AC. a good example is if you're comparing shield of Faith to protection from Good and evil.

[Unoriginal]

Im planning a character for a solo game - a fey wanderer ranger, with the following stat array and ACFs


Half elf
Revised ranger (Spell versatility, hunter's mark instead) 8
Fey wanderer
Feats (free feat at lvl 1)-resilient (con), stealthy (UA)

Scores
Str: 15 +1 +2 (racial+ASI) = 18
Dex: 13 +1 (feat) = 14
Con:10 +1 +1 (feat and racial) = 12
Int: 8
Wis: 14
Cha: 12 +2 (racial) = 14

Longsword, half plate

I get one uncommon magic item (mithral for my half plate to be a sneaky) and one rare (havent decided yet, probably a weapon)


The character is actually a paladin from a former game and edition who was revived after the event of said game.

Currently, with half plate, my AC stands in a respectable 17. Im cuurrently debating between sword-n-boarding it or taking a longsword/greatsword, and take the mariner combat style.


If I go for mariner Ill end up at 18, but if I take a shield I can get up to 3 more AC if I take a magical +2 shield. This raised the following question, at least for me. Obviously, there's quite a difference between 10 and 15 AC, or 13 and 18.

When does this difference stop mattering, if ever? Are these 3 points of AC gonna change something meaningful in the way the character acts, or if something could hit me on 18 it could also hit me on 21 and vice versa? (Not exactly, asking more in the general sense of things)

AC always matters, but on the other hand there is always a chance you get hit.

Practically speaking, though, most PCs are more than fine with a 17-18, and those with an higher AC can enjoy avoiding hits that would have flattened their teammates.

To put things in perspective: Demogorgon, the most powerful Demon in existence, and the Empyreans, who are literally half-gods (at least), both have 22 AC.



Now, any SANE DM wouldn't let you fight a red dragon solo, and only the most deranged ones let you fight it without magical gear.

A PC ending up in a difficult fight isn't a marker of the DM being insane.

[sophontteks]

If you want the utility of being able to climb and swim around unrestricted take mariner and a long sword. I'd recommend this simply because more AC is boring. Having a climb and swim speed gives you more options.

Combining your climb speed with grappling opens up some great options. Consider the prodigy feat with athletics.

[da newt]

The damage mitigation of AC is exponential as it goes up, but only matters for attack roles - saves don't care what your AC is, and AC damage mitigation is relative to the attack bonus of your foe because your effective AC is your AC - their attack bonus.

I have no experience with solo campaigns, but I'd think 20 AC and a d8 weapon would live much longer than a 17 AC and d12 weapon (especially in the lower levels), but a melee specialist may be much less effective than a spell slinger, summoner, or ranged fighter. Will you have any healing or temp hp capability?

I'd think for a similar style PC starting at lvl 8, an EK w/ shield spell, absorb elements, shadow blade, and SCAG cantrips would be more survivable.

[bendking]

Another thing to add to this is at a certain point getting a good source of disadvantage on incoming attacks is going to outweigh the cost of additional AC. a good example is if you're comparing shield of Faith to protection from Good and evil.

Umm... I don't know about that, considering AC actually has increasing returns the higher it is.

[x3n0n]

Umm... I don't know about that, considering AC actually has increasing returns the higher it is.

I think the claim requires a bit of context. With a 21 AC, a +10 attacker hits you on 11+, so 50% of the time, given a straight roll. With a 23 AC, that goes to 13+, or 40%. Imposing disadvantage with AC 21, the hit rate falls to 50% squared, or 25% (since both rolls need to be high enough to hit you).

The effect of disadvantage depends where you are on the "roll required to hit me" curve vs that enemy.

[da newt]

Umm... I don't know about that, considering AC actually has increasing returns the higher it is.

Can you think of an example where +3 to AC decreases your chances of taking a hit MORE than DISADV on all attacks?

The only examples I can think of are for VERY Lo ACs and/or VERY Hi to hit bonuses. With an AC of 8 and +4 to hit, that's 17/20 = 85% chance to hit. W/ 11 AC that would be 14/20 = 70%. AC of 8 w/ DISADV = .85*.85 = 72.25%

At better AC's I believe DISADV is always better. 20 AC, +4 to hit = 25%. 23 AC +4 to hit = 10%. 20 AC, +4 to hit, w/ DISADV = 6.25%

[stoutstien]

I think the claim requires a bit of context. With a 21 AC, a +10 attacker hits you on 11+, so 50% of the time, given a straight roll. With a 23 AC, that goes to 13+, or 40%. Imposing disadvantage with AC 21, the hit rate falls to 50% squared, or 25% (since both rolls need to be high enough to hit you).

The effect of disadvantage depends where you are on the "roll required to hit me" curve vs that enemy.

Aye. Even on the more extreme ends where an NPC only needs a five or more to hit you disadvantage stays ahead than a few points of AC.
Disadvantage also comes with the crit protection which if you're running solo is probably one of your biggest threats.

[Eldariel]

Ultimatively there is so much an experienced DM can aid you in slaying an unsurmountable foe, but if your Lv 15 butt is facing a dragon without magical aid or decent items? Nope out of there. No one in character would DARE to fight such monsters without proper preparations. Not even a 17th level ranger.

I'm pretty sure a level 13 Wizard would ultimately consider Dragon an annoying but an easily dealt-with brute. It's Huge, not Gargantuan, so all the usual Wizard tools for dealing with legendarily resistant creatures (Telekinesis, Bigby's, Forcecage, etc.) are in full effect. If it's not a spellcasting Dragon, it's susceptible to the usual "Forcecage + DoT" (or hell, just like...Chill Touching it dead if you have enough space; which given that it's a Huge creature is quite likely) even with zero magic items or anything. Of course, it's an exception among the classes.


Aye. Even on the more extreme ends where an NPC only needs a five or more to hit you disadvantage stays ahead than a few points of AC.
Disadvantage also comes with the crit protection which if you're running solo is probably one of your biggest threats.

OTOH, there are numerous sources of disadvantage while AC is quite a bit harder to buff.

[bendking]

I think the claim requires a bit of context. With a 21 AC, a +10 attacker hits you on 11+, so 50% of the time, given a straight roll. With a 23 AC, that goes to 13+, or 40%. Imposing disadvantage with AC 21, the hit rate falls to 50% squared, or 25% (since both rolls need to be high enough to hit you).

The effect of disadvantage depends where you are on the "roll required to hit me" curve vs that enemy.


Can you think of an example where +3 to AC decreases your chances of taking a hit MORE than DISADV on all attacks?

The only examples I can think of are for VERY Lo ACs and/or VERY Hi to hit bonuses. With an AC of 8 and +4 to hit, that's 17/20 = 85% chance to hit. W/ 11 AC that would be 14/20 = 70%. AC of 8 w/ DISADV = .85*.85 = 72.25%

At better AC's I believe DISADV is always better. 20 AC, +4 to hit = 25%. 23 AC +4 to hit = 10%. 20 AC, +4 to hit, w/ DISADV = 6.25%

My intention was that it was fallacious to claim that "there comes a point when imposing disadvantage is more effective than increasing AC", since it implies AC has diminishing returns, which is the opposite of true. Hoewever, I now see that I misread the original text, which referred to the price of increasing AC.
I did not claim that increasing AC is overall better than imposing disadvantage.

[x3n0n]

Aye. Even on the more extreme ends where an NPC only needs a five or more to hit you disadvantage stays ahead than a few points of AC.
Disadvantage also comes with the crit protection which if you're running solo is probably one of your biggest threats.

Yes, I should have mentioned crits: with disadvantage, they can only crit you 1/400 attacks, not 1/20.

Tying it back to OP: if you're willing to spend your rare item and an attunement slot on "preventing damage from attacks", a Cloak of Displacement plus a mundane Breastplate should get you hit much less frequently than the mithral half plate. (For that matter, the mundane breastplate plus the uncommon Cloak of Protection gets you the same AC as half-plate plus a +1 saving throw bonus, at the cost of an attunement slot).


OTOH, there are numerous sources of disadvantage while AC is quite a bit harder to buff.

Is there a good compilation of these somewhere? I just happened to remember the Cloak; the first that come to mind are always dodging, being unseen, imposing conditions on the attacker, or spells (Blur, PfG&E, Foresight, etc).

[RogueJK]

Is there a good compilation of these somewhere? I just happened to remember the Cloak; the first that come to mind are always dodging, being unseen, imposing conditions on the attacker, or spells (Blur, PfG&E, Foresight, etc).

Also other spells like Vicious Mockery, Bestow Curse, Eyebite, and Heat Metal, as well as Chill Touch against Undead, and Dispel Evil/Good against Celestials, Elementals, Fey, Fiends, and Undead.

Any spells/abilities that impose these conditions:
Restrained
Blinded
Frightened
Poisoned

Shoving an enemy Prone, combined with some way to set their movement to zero so they can't stand up (such as Grappling or Conquest Paladin aura)

Light Cleric's Warding Flare and Great Old One Warlock's Entropic Ward let you impose Disadvantage on one attack as a Reaction.

Similarly, Protection Fighting Style lets you spend your Reaction to impose Disadvantage on an attack roll made against an ally within 5 feet of you.

Battlemaster's Goading Attack and Paladin's Compelled Duel spell both impose Disadvantage on attacks against targets other than the Battlemaster/Paladin.

And then there's 3 levels of Exhaustion (which is hard to impose... 3 rounds within the radius of Sickening Radiance is the only way that comes to mind ATM)

[stoutstien]

My intention was that it was fallacious to claim that "there comes a point when imposing disadvantage is more effective than increasing AC", since it implies AC has diminishing returns, which is the opposite of true. Hoewever, I now see that I misread the original text, which referred to the price of increasing AC.
I did not claim that increasing AC is overall better than imposing disadvantage.

I should have been clearer about disadvantage acting as an amplifier for AC rather than a replacement. I just see it happen a lot of times when players focus on AC to a point they overlook simple ways to be tougher for less opportunity cost. Hence the SoF and prot G/E comparison.

For some reason most player know the power of advantage with attacks but fail to see how much it can impact mitigation.

[Pex]

Don't know yet what level it starts, but when your AC is 18 and you're getting hit nearly every round AC has become irrelevant. More so if your AC is 20. As a rule of thumb and round numbers I'd say you're good to level 10.

[Rusvul]

It's definitely true that each point of AC becomes progressively more powerful the more AC you already have. The difference between AC 12 and AC 14 is much less significant than the difference between AC 20 and AC 22.

However, in very high level campaigns, there can come a point where AC becomes less useful as a defense. In one absurdly over-the-top game in particular, I played a character minmaxed all to hell with an artifact shield, and my AC was consistently 30+... but when every enemy is a dragon with a DC 22 breath weapon and +19 to hit, the value of a high AC decreases considerably.

That's a rather niche circumstance, though. While it can happen, within the scope of how people actually play the game 99% of the time, AC 17 will pretty much always be adequate, and AC 20+ will always offer pretty notable protection from attack rolls.