The 65% accuracy myth

One tool that theorycrafters often utilize is the assumption that you will hit 65% of the time on average. This assumption makes sense given that the designers have stated that they aim for players to hit ~65% of the time when facing a foe of the appropriate challenge rating. But how does this hold up in actual play?

So if we assume that the 65% number is correct, then you are expected to hit a foe whose CR = your level roughly 65% of the time. And if your party of four has 6-8 medium encounters per day against a single foe whose CR equals your level, then you will hit 65% of the time on average. But that should almost never happen in practice. In general, you should be fighting multiple foes.

Because of XP multipliers, more foes means drastically more difficult encounters. An encounter with just two foes whose CR = your level will often be super deadly and use up roughly half of your daily XP budget. In general you should be facing 4-6 foes at once in most encounters.

In general, an encounter against 4 foes whose CR is equal to half your level will be a deadly encounter and use up roughly 1/3 of your daily XP budget. With six foes, a deadly encounter usually involves foes whose CR is equal to half your level -1 or -2. These are rough guidelines, but hold true for most levels of play.

So what does this mean for the 65% accuracy number? Well, lower CR foes have lower AC. When facing groups of foes, this generally results in enemies with an AC about 1 to 3 points lower than a foe whose CR is equal to your level.

Conversely, if you are facing a single foe who has a higher CR than your level, their AC will be higher than expected. In general, if you want a single foe to be a Deadly encounter for a party of 4, the foe needs to have a CR roughly 2 to 4 higher than the party's level. This results in a typical "boss monster" having roughly 1 more AC than expected. Though to be honest, the action economy of 5e makes single boss monsters somewhat of a joke, and they should still be backed up by lower CR minions.

All together, this means that in general, most of the attacks you make will be against foes whose CR is lower than your level. As such, most of the attacks you make will be against foes whose AC is lower than expected, raising your total accuracy above the 65% baseline.

Another issue the 65% accuracy baseline faces is the fact that magic items exist. Monster math does not assume that magic items exist. But random treasure tables, modules, and other sources provide magic items to players with a fairly high degree of frequency. You are likely to have a +1 or better weapon by level 9+. And you are likely to have a +2 weapon or better by level 17+.

If you have a +X magic weapon, your accuracy will be higher than expected against foes whose CR is equal to your level. And most parties will find +X weapon at some point. This will boost your accuracy above the 65% baseline.

Finally, we need to take a good hard look at [monster stats by level](https://i0.wp.com/theangrygm.com/wp-content/uploads/2019/10/MonsterStatsByTier.png?ssl=1) (Thanks to the angry GM for putting the monster stats by CR into a nice easy to read table). So far we have been trusting the statement that you are supposed to hit 65% of the time when facing a foe whose CR = your level.

But if we compare that table (or any analysis that takes the average monster AC by CR), we find something interesting. If you have an 18 attribute by 4th level, and a 20 by 8th level, you actually hit a foe whose CR is equal to your level on a 7+ for half of the levels of play. So half of the time, your accuracy is 65% and the other half it is 70%. And again, this does not include magic items.

So what does this all tell us?

First off, your accuracy is actually around 65%-70% on average when facing foes whose level is equal to your CR. This of course fluctuates somewhat, as not all monsters have an AC that is the average for their CR. But in general, using 65-70% as your accuracy baseline is not a bad plan if you plan to only face enemies whose CR is equal to your level.

Secondly, only facing enemies whose CR is equal to your level is generally a bad assumption. To use up the adventuring day budget would require 6-8 encounters each against a single foe, or 2 encounters against two foes. Neither prospect will lead to fun or enjoyable adventuring days. The best solution is then to have a few encounters each day, with roughly 4-6 foes each (and hopefully some variety of foes as well such as soldier, brutes, artillery, controllers, skirmishers, and the like).

Third, when you face multiple foes in an encounter, XP multipliers mean that you generally face monsters whose CR is much lower than your level. Again, in general, a group of 4 foes whose CR is half your level leads to a deadly encounter that will use up 1/3 of your daily XP budget. And when facing foes whose CR is half your level, their AC will generally be 1-3 points lower than the baseline assumptions. Even if you face the occasional solo boss monster, their AC will normally only be 1 higher than expected. And you typically will have to get through the bosses minions first. So most enemies you face, and most attacks you make, will be made against ACs lower than the baseline assumes.

Finally, magic items exist. And any +X item you have will boost your AC above the baseline.

So when calculating damage output with our shiny new 1D&D toys, make sure account for the accuracy that makes the most sense at your table. If you only fight foes whose CR is equal to your level or higher, and you never have +X weapons, then using a 65% baseline accuracy might be appropriate. But if your table regularly fight groups of enemies or you consistently have a +1 weapon by level 5, make sure you boost that accuracy number up a notch or two.