How do +X weapons/armor affect monster CR?

[Oramac]

Before I start, I'm not the best in the world at math, so please forgive me.

Ok, so we've all heard the phrase "5e is designed with no magic items in mind", right? So if you give a player, say, a +1 sword and a set of +1 armor, isn't that basically the same as reducing all monsters AC and to-hit bonus by 1?

If so, how does that affect CR at the +1/2/3 bonus levels?

Short version: if a party of 4 all have, for example, +2 weapons and armor, is it then appropriate to use monsters that are 2 CR higher than normal?

[JackPhoenix]

Not necessarily, and the value of the bonus varies depending on the party level: having +1 weapon is a big deal at level 1 (about 20% increase in combat ability), at level 20, not so much (less than 10% increase).

There isn't any exact guideline... yes, party with magic equipment is more powerful, but balancing encounters is more art than science already (and CR doesn't really play a role in that, it's all about xp)

[PhoenixPhyre]

There isn't any exact guideline... yes, party with magic equipment is more powerful, but balancing encounters is more art than science already (and CR doesn't really play a role in that, it's all about xp)

But doesn't CR determine XP? As in, CR X enemies are worth Y XP? This is just a quibble, because otherwise I agree. I tend to estimate that a party with class-appropriate +1/+2 gear are about 1-2 levels higher than they really are. A wizard with a +3 longsword isn't much better, but a monk with a staff of striking is lots better (made the mistake of giving a level 9 one once...thought it was only +1 or +2. Then looked at the book and saw it was a +3. Ouch).

[Waterdeep Merch]

If the party has at least one +1-equivalent piece of gear per player pre-level 5, I amp the CR by 1.

If the party has at least one +2-equivalent piece of gear per player pre-level 11, I amp the CR by 1.

If the party has at least one +3-equivalent piece of gear per player pre-level 15, I amp the CR by 1.

If the party has any sort of legendary-equivalent gear, I amp the CR by 1 per piece.

These must be things they actually use regularly, of course. As PhoenixPhyre pointed out, a (non-bladesinger) wizard with a magic longsword isn't appreciably better because they're unlikely to use it much. In cases where it isn't the entire party, I lean more heavily towards the hard/deadly side of the encounter tables to balance things out.

[Vaz]

CR is a crap determinate of giving XP. It is providing a value to XP that XP already provides. CR could easily be replaced with XP as a stat for no difference.

A TRex is not a challenge for a group of 4 8th level party members, especially those which can fly or use ranged attacks or use horses and use range. The numbers they arbitrarily throw on things are a bit of a joke i think. Ignore them.

Eyeball it. Practise. Easy = less than an 8 to hit/pass, hard = greater than 12. Math the average; if players can do X on average rolls, and kill it before it kills them on expected resources after time in the day, then they are fine.

The worst thing you can do is give them mlre exp making you give them more dangerous stuff to fight later on.

[mephnick]

It's much more important to know your players. My regular players have all been playing D&D for years and optimize strategy natually, so using the encounter guidelines in the DMG almost always makes for a cakewalk. My side group is newer casual players and DMG guidelines are more than enough to challenge them. The amount a good powerful item will effect things can vary greatly between the groups. Like said before, art over science.

[JackPhoenix]

But doesn't CR determine XP? As in, CR X enemies are worth Y XP? This is just a quibble, because otherwise I agree. I tend to estimate that a party with class-appropriate +1/+2 gear are about 1-2 levels higher than they really are. A wizard with a +3 longsword isn't much better, but a monk with a staff of striking is lots better (made the mistake of giving a level 9 one once...thought it was only +1 or +2. Then looked at the book and saw it was a +3. Ouch).

Mostly, it's misleading. Differences between CR are not equal. Similar to the value of +1 bonus at various character levels, there's huge difference between the "value" of CR difference at various levels. Sending CR 2 instead of CR 1 creature against level 1 party may be the difference between wipe and successful fight (I mean, even a bugbear can be nasty at that level, but compared to, say, ogre? Of course, the game is nowhere near balanced at level 1, so there's that), at level, say, 17, you won't really notice if what you're fighting is CR 19 or CR 21. The encounter building also causes misunderstanding... see the other thread where someone said "HotDQ sends CR 32 encounter against low level party!", but while 4x CR 8 assassins are too powerful for the low-level characters in any case (and noted as a result of assassin's stats changing between writing of the adventure and MM release), xp (and thus, encounter building) -wise, they are equivalent of CR 21 creature (with adjusted xp for 4 creatures, without the xp adjustment, they fit somewhere between CR 15-16)

[Vogonjeltz]

Before I start, I'm not the best in the world at math, so please forgive me.

Ok, so we've all heard the phrase "5e is designed with no magic items in mind", right? So if you give a player, say, a +1 sword and a set of +1 armor, isn't that basically the same as reducing all monsters AC and to-hit bonus by 1?

If so, how does that affect CR at the +1/2/3 bonus levels?

Short version: if a party of 4 all have, for example, +2 weapons and armor, is it then appropriate to use monsters that are 2 CR higher than normal?

Your title is misleading, it sounds like you're asking if giving the monster equipment would change its CR (the answer to that is obviously, Yes; DMG 274).

The party having more equipment has no bearing on the appropriateness of encounters.
Encounter difficulty is entirely a function of the number of characters in a party and each of their levels. (DMG 82, XP Thresholds)

It's inappropriate (from a balance point of view) to change encounter difficulty based on what the party has in equipment.

[Vaz]

If they had gear to triviliase X encounter, then X encounter is virtually pointless. Why give a group of all flying party members a challenge to scale a mountain?

[Zalabim]

To address the example more directly, giving the entire party +2 to hit and +2 to AC is like dropping the monster AC and Attack Bonus by 2, which drops Offensive and Defensive CR by 1, which drops overall CR by 1. So it would only be -1 to CR of opponents rather than -2. There would still be enemies that are a certain CR because of special abilities that PCs couldn't counter, or because of relying primarily on saving throw effects which would remain unchanged. There would also be enemies whose HP is partially based on having resistance to non-magic weapons and they'd actually have their defensive CR lowered a little more.

There really isn't a blanket rule that can be applied.