What is the difference between giving advantage on a roll and reducing the DC?

Question

I run a 5e campaign, and I like rewarding my players for thinking outside the box, roleplaying well, etc. Suppose we have the following scenario:

Violet is a bard, and is attempting to intimidate a city guard while they are alone. The nearby torches suddenly dim and flicker uncertainly. Various objects shake violently and fly about the room, crashing into the walls, tables, and each other. Violet makes a wonderfully scary and venomous threat to the guard.

Violet’s use of fun bard spells and the good roleplaying was great, and I want to reward her player on the Intimidation roll.

I see two possible ways to do this:

• Grant the player advantage on whatever roll they’re making
• Reduce the DC of the check (but by how much?)

How do these two methods differ from one another? Are there scenarios when one is preferred over the other?

Answer 1

Mechanically, I would say the main difference is that advantage is easier and provides more stable results (As your result chances go from evenly distributed, to a favorably skewed curve). 5e favors using advantage/disadvantage as a quick, simple, effective way to deal with temporary bonuses.

Narratively, advantage is a temporary bonus to one action, while a change in DC is a change in the difficulty of the task being attempted.

Giving Advantage means the task is harder for Violet to fail

This means, narratively, that thanks to Violet's special effects, the guard will be more likely to be intimidated by the next thing that comes out of Violet's mouth. The bonus is only for Violet's next action (or until the effect that gives Violet advantage no longer applies to the situation).

Changing the DC means the task has changed

This would mean the guard has lost their composure, and they will think everything is more intimidating/scary. In this case, the bonus applies to Violet and to anyone else attempting the same task.

As another example, building a partial bridge over a gap doesn't make jumping over easier; the jump you have to do to get across is now an easier task for everybody.

Answer 2

Just give advantage

I’ll get to the math in a minute, but the math really should be moot: there is no guidance for altering DCs based on PC actions because the point of the advantage mechanic is to eliminate the hundreds of ways of tweaking situational probability.

Advantage (and disadvantage) exist entirely to handle exactly these sorts of situations. Avoiding using it is fine if you’re into homebrewing your game rules, but if you’re wanting to just use the methods the game provides, give advantage.

The math, in very brief

Advantage is equivalent to reducing a DC by 5… sometimes. That’s the average case. How much advantage is actually worth depends on what your original DC and roll bonus are, because the probability for the highest of two dice beating a target number is a curve instead of a straight line.

Answer 3

Advantage is the usual way

DnD 5e seldom uses situational modifiers to rolls. Advantage is the usual way for the system to describe something is particularly easy because of some circumstance. Advantage is more conventional than lowering the DC, and your players are more likely to be used to it than changing modifiers or DCs.

Advantage is more transparent

Unless you tell the player that the DC has changed, they won't know their cool plan had any effect. Advantage on the roll is transparent and serves as a good reward for playing the character's strengths well.

Advantage affects the numbers more smoothly

Having advantage on a roll squares your chance of failure. Importantly, this means failure never becomes impossible because of advantage. Lowering the DC or granting a bonus modifier is just a flat decrease in the failure chance of five percent points per point of DC decreased - and notably, this can reduce the chance of failure to zero (especially if the Bard in question has Expertise in Intimidation).

Overall, Advantage is the way to go. It's clear, it's the usual way to do it in 5e, and it changes the probabilities smoother than changing the DC.

Answer 4

This is partly DM prerogative, but the Dungeon Master's guide does give handy guidelines.

The DC is typically more of a fixed thing, representing the difficulty of the task (though still set by the rules or the DM). For arbitrary tasks it gives some examples such as:

Easy = 10, Medium = 15, Hard = 20

However, the DMs guide speaks of advantage and disadvantage. There it says:

They reflect temporary circumstances that might affect the chances of a character succeeding or failing at a task. Advantage is also a great way to reward a player who shows exceptional creativity in play.

This quote sounds like it answers your question.

Giving advantage avoids any issues of trying to add up or subtract a whole bunch of DC modifiers; it is much more straightforward.

Answer 5

The task has not become easier, the bard just did a super good job. Because of that I think advantage is better. DC is how difficult a task is.

Here's an example of using a lower DC to intimidate a guard.

Player: Violet looks at the guard. She want so size him up to see if he is a tough guy.

DM: Roll Wisdom (Insight).

Player: Nice, 18!

DM: This guard has a big scar over his face and looks like he's seen a thing or two in this town.

Player: Yikes! Violet checks another entrance.

[...]

Player: Okay, Violet also sizes this guy up, I rolled another 18 on Wisdom (Insight), does she learn anything?

DM: This guard looks nervous. He looks to his side as he seems to hear something. A rat darts across the path. He jumps a little and quickly looks around to see if anyone saw him lose his cool.

Player: Perfect...

Since Violet is about to intimidate a guard who is more easily frightened I'd reduce the DC here instead of giving advantage. (However, if she still did the super cool stuff with her magic I would also still give advantage.)

Answer 6

As mentioned by SSD and kviiri, there is some mathematical difference, mainly in that Advantage is consistent and you don't need to calculate by how much you will change the DC.

Tezra also gives a good answer on the interpretation of it: Advantage means the character has some help, something that makes the task easier. A character climbing with a rope has advantage. Climbing something with no inclination has a small/no DC.

I will disagree with the two most upvoted answers, though, in that your scenario seems to be more about the Guard getting more scared of anything than of specifically Violet - but that is my interpretation of how I imagine the guard reacting¹. Although mechanically advantage is easier, straight-forward and the standard way in 5e, this specific scenario might call for a reduction of DC.

A similar case happens in Lost Mine of Phandelver, where feeding the hungry and angry wolves will make the DC to calm them down lower, not only give advantage to the person who fed them. That's to say there is precedent in the published adventures for reducing the DC.

A character who tries to calm the animals can attempt a DC 15 Wisdom (Animal Handling) check. On a success, the wolves allow the character to move throughout the room. If the wolves are given food, the DC drops to 10.

Also, there is one mechanical difference that seems to not be mentioned until now: Advantages do not stack, additive bonus do - so, if you give a -5 to the DC, you can later on, because of some other action, give another -5 to the DC. If you give advantage, you will not be able to give another advantage later on. Note that this is intended to reduce the bean counting, in opposition to what happened in earlier editions.

Either way, a good rule of thumb, as mentioned by Tezra, is: If the task became easier (or harder) to everyone, or if you essentially changed the task, the DC changes. If someone has some kind of particularity that will help them specifically, give them advantage. In your scenario, say the guard is scared of Undeads and Violet disguises herself as a Zombie. That would be a clear advantage case.

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¹ To be clear, I'm imagining the guard becoming kinda paranoid and jumping scared even if a cat meow'd at him after all of this "supernatural" stuff, mostly because I'm imagining the guard does not know/understand that the bard is the one causing all this stuff and is pinning it on some supernatural stuff, like a cliche horror movie.

Answer 7

There is a significant mathematical difference between giving advantage (or disadvantage) and decreasing (or increasing) the DC of a task or the AC of a monster for attack roles. Knowing the difference may help you to decide when one is more or less appropriate.

The math behind increasing and decreasing Difficulty Class (DC) or armor class is fairly simple. Each bonus or penalty of +1 or -1 changes the probability on a d20 roll by 1 in 20, or 5%. It's a scalar linear progression, 5% harder or easier per point. You can always count on the task being the same difficulty for whoever attempts it.

Advantage/Disadvantage is a bit different. When rolling with Advantage, the odds of getting X or better is much easier when X is low. And becomes slightly less advantageous as the desired roll of the die becomes larger. For instance, there is a 5% chance of rolling a 2 or better on a d20, but with advantage that 5% gets you about a 7 or better. So you're getting about a +5. However as that desired number increases that percentage of difference decreases, so that once you're needing a 14 or 15 or 16 it's only about a +3, 16 or 17 about a +2, 18 or 19 about a +1. Getting a natural 20 is easier (about half of a 5% +1 bonus worth). Disadvantage is similar but in reverse. It's the equivalent of a very low penalty about -1 (5% penaly) when you need a low number, and eventually becomes a much more devastating -4 to -5 at the very high end of the scale. So what does this mean? It means when you are a high level or have a high skill relative to the challenge you are facing and you don't need a really high roll, advantage helps you out a whole lot! About +4 or +5 (20% or 25%)! When you are a low level with low skill and you need to roll high, advantage helps out... but not so much. Maybe equivalent to a +1 or +2. (5% or 10%). Likewise, disadvantage isn't so bad for highly skilled rolls against a relatively easy difficulty class. About a -1 or -2. But when you suck and you need to roll high, disadvantage is equivalent to a devastating -4 or -5.

When a task becomes easier due to factors that are likely to be noticed and taken advantage of by skilled heroes, but likely missed by more novice heroes, advantage makes more sense than tweaking difficulty class. When the task is suddenly likely to be extremely hard for a novice but only neligibly harder for an expert, Disadvantage makes sense.

DC represents an across the board change in difficulty for ALL characters. Advantage or Disadvantage makes more sense when the relative expertise of the character is likely to have a profound effect on the likely percentage bonus they are going to receive (reflected by the number likely to be rolled). I hope that helps. Happy hunting, intrepid adventures.