What's the math and theory on targeting saves vs A/C?

[MarkVIIIMarc]

All this spell list talk has me thinking about all these spells which target saves vs A/C and at what point you stand a better chance of hitting the opponent.

Obviously more choices are better and I have access to spells which target a variety of saves. A/C is something which can be targeted also

I see a variance between 12 and 22 commonly for A/C. Victim saves seem to have a similar range between -2 and 9 or so.

At Level 10 I think a Save DC of 19 is easy enough and what, maybe 9 for a Spell Attack Modifier. To Hit bonuses can easily be 9 also.

So when is it better to target a particular save vs armor class?

[NNescio]

All this spell list talk has me thinking about all these spells which target saves vs A/C and at what point you stand a better chance of hitting the opponent.

Obviously more choices are better and I have access to spells which target a variety of saves. A/C is something which can be targeted also

I see a variance between 12 and 22 commonly for A/C. Victim saves seem to have a similar range between -2 and 9 or so.

At Level 10 I think a Save DC of 19 is easy enough and what, maybe 9 for a Spell Attack Modifier. To Hit bonuses can easily be 9 also.

So when is it better to target a particular save vs armor class?

Mathematically, roughly when Save DC + AC - attack bonus - save bonus > 22, all else being equal. (i.e. both a hit and a failed save has the same effect.) This also ignores advantage/disadvantage and crits and Nat 1s (and other effects that monkey with rolls, like Portent, Lucky and Legendary Resistance), so it's not entirely accurate.

('Attacker's' Save DC, Defender's AC, Attacker's attack bonus, Defender's save bonus)

If we assume the 'attacker' adds the same proficiency and ability bonuses to both Save DC and attack rolls (which is true for most spellcasters), then the rough formula becomes:

AC - save bonus + misc. Save DC bonuses - misc. attack bonuses > 14

And if we assume there are no magic items or class features or other effects that grant misc. bonuses:

AC > 14 + save bonus

Which basically means "don't bother with Save spells unless you can target a weak save, or if the Save spell still has a partial effect on Save, or if you can hit multiple creatures with the same spell, or if you have some way to guarantee a failed save (or at least severely penalize the opponent's roll), or if the failed save is so debilitating that it practically wins the encounter anyway" (or if the target has an abnormally high AC for its CR, but that's uncommon and isn't something the player can really control) because targeting Saves is generally less reliable than targeting AC. But a lot of Save spells fulfill at least one of the "unless" clauses above, so they are still often worthwhile. Not for most cantrips though.

Also Con save spells tend to suck because most things in the MM have high Con and Con save proficiency. More so for the mook-type enemies (minions/adds) that don't justify spending a spell slot on (unless you can hit multiples with an AoE), so Con-save cantrips suck even more.

Int save spells on the other hand are stellar. And Int save cantrips work excellent against mooks because those are even more likely to have poor Int saves.

[Crgaston]

Good Stuff

Nice, thanks for that.
Pardon my ignorance/laziness, but what cantrips have Int saves?

[NNescio]

Nice, thanks for that.
Pardon my ignorance/laziness, but what cantrips have Int saves?

No officially-released* ones yet, but Mind Sliver from Unearthed Arcana: Sorcerer and Warlock does exactly that. The 2019 Unearthed Arcana: Artificer also has a pseudo-cantrip in the form of the Archivist subclass' Information Overload ability.

(UA doesn't count as "released" because it's playtest.)

Yes, most people say these cantrips (pseudo-cantrip included) are OP.

[AdAstra]

It's very simple in practice. If you do the math, it works out to:

-Assuming the ability modifier used for the attack/save DC is the same or equal (IE +3 wisdom and strength mod)
-A +0 to a save is equivalent to 14 AC in terms of chance to succeed for the attacker. (if save DC is 13 and attack bonus is +5, then the attack has a 60% chance to hit, and the save has a 60% chance to be a failure) This is also a purely linear relationship, so +1 to a save is equivalent to +1 to AC.
-So to convert a save modifier to "AC-Equivalent", just add 14 to the save modifier.
-To put this in concrete terms, a +4 to a save is equivalent to plate armor (18 AC). A +7 is equivalent to plate armor, a shield, and the Defense fighting style (21 AC). A +12 is equivalent to all that and a casting of the Shield spell (26 AC).

Haven't done a detailed analysis, but my gut and experience would tell me that targeting a monster's strong saves is usually worse than attacking, while targeting their weak saves is usually better. If the monster's AC is particularly high, then even targeting strong saves is probably about as viable as attacking.

Wonder if anyone will start referring to monster's ACE for a given stat. Hope so, it would probably help with optimization discussion and inflate my ego.

[dragoeniex]

All this spell list talk has me thinking about all these spells which target saves vs A/C and at what point you stand a better chance of hitting the opponent.

Obviously more choices are better and I have access to spells which target a variety of saves. A/C is something which can be targeted also

I see a variance between 12 and 22 commonly for A/C. Victim saves seem to have a similar range between -2 and 9 or so.

At Level 10 I think a Save DC of 19 is easy enough and what, maybe 9 for a Spell Attack Modifier. To Hit bonuses can easily be 9 also.

So when is it better to target a particular save vs armor class?

Bouncing off what AdAstra said, it really depends on the monster you're up against and which saves you're forcing. Are you comparing whether it's better for casters specifically to target saves vs AC, or just in general?

As a caster, as you go higher and higher, most of your offensive, levelled spells are going to involve saves, while very few will ask for an attack roll. Even Planeshift requires a save after you land the attack if you try to force it, and the to-hit portion seems to be there exclusively to make it not-entirely-easy to fling foes into hellscapes with a single touch.

Save spells also typically give you more impactful effects or the ability to target more than one creature. These become your bread and butter pretty early on, with cantrips as the main exception.

Also, how are you getting 19 DC by character level 10? A caster who has maxed-out their main stat but has no DC-increasing items (which are very, very rare to come by with exception to warlocks and their rods) will reach DC 19 at character level 17 and stay there.

[MarkVIIIMarc]

Bouncing off what AdAstra said, it really depends on the monster you're up against and which saves you're forcing. Are you comparing whether it's better for casters specifically to target saves vs AC, or just in general?

As a caster, as you go higher and higher, most of your offensive, levelled spells are going to involve saves, while very few will ask for an attack roll. Even Planeshift requires a save after you land the attack if you try to force it, and the to-hit portion seems to be there exclusively to make it not-entirely-easy to fling foes into hellscapes with a single touch.

Save spells also typically give you more impactful effects or the ability to target more than one creature. These become your bread and butter pretty early on, with cantrips as the main exception.

Also, how are you getting 19 DC by character level 10? A caster who has maxed-out their main stat but has no DC-increasing items (which are very, very rare to come by with exception to warlocks and their rods) will reach DC 19 at character level 17 and stay there.

I typo'd the save. Its a DC 17 save @ level 10.

[LudicSavant]

Nice, thanks for that.
Pardon my ignorance/laziness, but what cantrips have Int saves?

No cantrips have Int saves.

The spells with Int saves are Phantasmal Force, Enemies Abound, Contact Other Plane, Synaptic Static, Mental Prison, Symbol, Feeblemind, Illusory Dragon, and Psychic Scream.

[MarkVIIIMarc]

No cantrips have Int saves.

The spells with Int saves are Phantasmal Force, Enemies Abound, Contact Other Plane, Synaptic Static, Mental Prison, Symbol, Feeblemind, Illusory Dragon, and Psychic Scream.

THAT is a useful list. I think all DM's should have it for a creature called the Anti-Int-Dump monster folks will encounter various sizes of several times over a campaign.

Afterall, you would think the type of ppl who go diving into dungeons are maybe low on Wisdom types lol.

[diplomancer]

Maze has a DC 20 int check, which is harder than a save.

I was very happy as a Paladin when the final boss of the campaign cast Maze on me, instead of on my Steed, as I could simply use the Cleansing Touch ability on myself to get rid of it. If my steed had been put in the maze it would have been rough (it was a Pegasus so at least there was a 5% chance)


It's very simple in practice. If you do the math, it works out to:

-Assuming the ability modifier used for the attack/save DC is the same or equal (IE +3 wisdom and strength mod)
-A +0 to a save is equivalent to 14 AC in terms of chance to succeed for the attacker. (if save DC is 13 and attack bonus is +5, then the attack has a 60% chance to hit, and the save has a 60% chance to be a failure) This is also a purely linear relationship, so +1 to a save is equivalent to +1 to AC.
-So to convert a save modifier to "AC-Equivalent", just add 14 to the save modifier.
-To put this in concrete terms, a +4 to a save is equivalent to plate armor (18 AC). A +7 is equivalent to plate armor, a shield, and the Defense fighting style (21 AC). A +12 is equivalent to all that and a casting of the Shield spell (26 AC).

Haven't done a detailed analysis, but my gut and experience would tell me that targeting a monster's strong saves is usually worse than attacking, while targeting their weak saves is usually better. If the monster's AC is particularly high, then even targeting strong saves is probably about as viable as attacking.

Wonder if anyone will start referring to monster's ACE for a given stat. Hope so, it would probably help with optimization discussion and inflate my ego.

I don't know about others, but I like this so much that for myself I will try to use it regularly.