Setting Difficulty Class (DC) in DnD5e – stating the obvious

I’m working through my Grappling Smackdown scenario here, and setting the DCs for various tasks is a thing. I wanted to make a table to quickly inform me of roughly how hard something might be, so I figured I’d share the results. This isn’t a revelation, but it’s useful to me so it might be useful to you.

One useful tidbit from the post on The Standard Array: Joe Human PC with the standard array and who is proficient in a given task will sport a 13.5 attribute as a median, and of course have a +2 proficiency bonus. This makes the average starting boosts to the die rolls about +3.5.

I’ve picked out some example DCs. Obviously moving the DC up or down a point changes the odds of success (on the average) by 5%.

DC 6

At this level, a potted plant that isn’t proficient in the skill has a 50% chance of noticing something or accomplishing a task. I’m having to significantly question why bother rolling at all here. It’s a level that might get interesting if due to unfavorable terrain or darkness or something everyone gets disadvantage.

DC 8

A first level, proficient character with a 10 ability score will still succeed 75% of the time, or a non-proficient character with a 14, a solid but not exceptional DX, for example. This is a good level for a simple task which requires some talent or expertise to get through, but by and large will be a speed bump. Even my potted plant, above (-5 ability score, not proficient) if allowed a roll will succeed on a 13 or higher, 40% of the time.

DC 11

This is still an entry level task, where a completely non-proficient average guy can succeed 50% of the time. The median starting human PC will be succeeding on this by rolling an 8, so 65% chance of success. There’s only a 10% chance of failure for a typical proficient 10th level PC operating in the expert zone. A DC 11 means that it’s still expected most folks will do this well, but the odds of failure for the uninitiated are high.

At DC 11 and DC 12, a non-proficient character rolling against one of their lowest two ability scores (9-11 as a human) will more or less have a 50% chance of success. So it’s the dividing line for “requires some sort of atypical ability or advantage to succeed better than half the time.” Atypical for PCs, that is.

DC 14

Odds of a median first through fourth level PC who is proficient in the skill failing this roll is about 50%. At this level if you’re positing (say) a forked path for adventurers of 1st through 4th level (+2 proficiency), you’re basically saying “flip a coin.” I feel this is a pretty important DC level, as it sets the boundaries for making decisions in adventures. Want your “secret pathway” to come up about half the time? That’s about a DC 14 check . . . but you better be darn sure you have it in your mind that if everyone is allowed a roll, half the median party will fail, and half will succeed, assuming their attributes and skills are spread around a bit.

Anything harder than DC 14 will require advantage, high attributes, and high proficiency to make it a cake-walk. For example, a +4 bonus and +4 proficiency, given as a 10th level character with an 18 or 19 ability score, will still fail this check 25% of the time, although if they have expertise or can eke out advantage from somewhere, they’ll only fail if they crit.

DC 17

Now you’re into telling the GM and PCs you expect them to fail. A first level PC will need to roll 14 or higher to succeed here, and even our hypothetical +8 bonus 10th level proficient character will need to roll 9 or higher (60%). An untrained person using their “dump stat” of (say) 9 or 10 will have a 75-80% failure rate here. Only a true expert (has Expertise in the skill) at high proficiency with an outstanding ability score will be looking at this as trivial.

DC 17, though, is also the level where your low-level party expert (+2 proficiency, +4 in their chosen skill at 4th level due to an ability score improvement) has a 50% chance of success. So much as DC 11 or 12 is the dividing line for making it hard for the unskilled, DC 17 is the line above which only the truly exceptional will succeed more than they fail.

DC 21

Now you’re just being mean. You need +5 proficiency, +5 attribute score, and you have a 50% chance of making this. It’s the break-even for high-level, high-skill “this is still hard” tests. At low level, you’re saying “only a crit will get you here, and only if you have a bonus, at that.” Again, one has to ask why bother unless it’s something that you think the PCs might try but it’ll be pretty silly. Well, yes, you could leap the chasm, but it’s DC 21 . . . chances of success are low.

Parting Shot

So, hopefully this will be of use as a quick reference, if nothing else. Good ability score bonuses to keep in mind are probably +0 (dump stat), +1.5 (median starting character), +3 (expert starting character), and +5 (fully developed unless you’re breaking the 20-maximum rule, as some classes do). Proficiencies are +2 (starting), +4 (mid-level), and +6 (pinnacle). Figure out how likely you want success to be, and adjust from there. Ergo, a handy table. Well, handy for me.

Ability Score Proficiency 25% Success 50% success 75% Success
0 2 18 13 8
0 4 20 15 10
0 6 22 17 12
1.5 2 19.5 14.5 9.5
1.5 4 21.5 16.5 11.5
1.5 6 23.5 18.5 13.5
3 2 21 16 11
3 4 23 18 13
3 6 25 20 15
5 2 23 18 13
5 4 25 20 15
5 6 27 22 17

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