Not everything that’s part of D&D is an official mechanic. Some things we discuss are much more conceptual in nature. That’s the case for the theory of bounded accuracy, a driving force behind the mechanics of 5e D&D.
In this article, we’ll discuss what this concept is and how it affects your games.
What is Bounded Accuracy?
Bounded accuracy is a design principle in 5e D&D that limits the numeric bonuses we add to our d20-based rolls. Changes made to the bonuses from previous editions allow us to focus more on how many hits a character can take and what abilities they have, rather than just looking at the numbers.
The term itself is pretty simple. “Bounded” means to be restricted within certain limits, while “accuracy” refers to how hard it is to do something. Put them together and we get: “A set of limits on how hard it can be to do something.”
When we look at the roll of a d20, there are 20 different options. Shocker, right? It’s the basis of how we decide whether or not we’re capable of doing something.
If bonuses didn’t exist at all, we’d be looking at a system where everyone had the same chance of succeeding on a task whenever they roll the dice. We’d also never be able to roll anything above a 20, that would be impossible.
In 5e, we do have bonuses, but they’re not as insane as they have been in previous editions. Now we have some limits as to how high of a roll you can get, or how good you can be at something. Naturally, the question is, what are those limits?
What are the Limits in 5e?
The highest roll possible for your average character in 5e is a 30. That number is arrived at by combining our natural dice rolls with any modifiers available. This creates consistency, setting 30 as the maximum DC, AC, and CR throughout 5e.
Natural Dice Rolls. On a d20, there are actually only 18 numbers we care about. Since a 1 is a critical failure and a 20 is a critical success, it’s everything in the middle that actually gets brought into calculation. This means that the highest roll that counts on a d20 is typically a 19.
Proficiency. In 5e, every character has the same progression for proficiency bonuses. These bonuses start at 1st level with +2 and end at 20th level with +6. There are a few classes that get the expertise ability, allowing them to add their bonus twice, but we’ll treat this as an outlier.
Ability Modifier. Characters in 5e have an ability score cap of 20, meaning they won’t pass above a +5 modifier except for in extremely specific circumstances.
How Does Accuracy Work in 5e?
The modifiers we apply to any roll of the d20 let us know how good we are at doing something. Since the typical maximum modifier is 11, our scale of possibilities is anywhere from -3 to 30. This gives us a relatively small range to determine the difficulty of a task.
It’s for this reason that any check requiring the roll of a d20 can be split into the following table.
Anything more difficult than hard is going to require critical success or some impressive modifiers, but in theory there’s nothing we deal with that is so insane that we need anything more than the normal modifiers available through level progression.
The Impacts of Bounded Accuracy
Bounded accuracy transcends more than just the role of dice in our games. Everything from the creatures we fight to the traps we encounter are affected by this theory of game design, and understanding it can make you a better player and DM.
The following are a few different sections of the game where we see the influence of bounded accuracy.
- Ability Checks
- Character Progression
- Magical Items
This is probably the most straightforward effect. Bounded accuracy allows the DC table above to be consistently accurate throughout the game. The table accounts for how hard it is for an average commoner to do anything within the mechanics of 5e.
Your average Joe commoner has an ability score of 10 in every ability, meaning he has no modifiers. When Joe rolls a die, he deals with the result.
Our player characters tend to start out with a bit more skill. They’ll likely have an ability that they can add a decent modifier to along with their proficiency bonus. Jackie, a level 1 elven rogue with a dexterity score of 16 and proficiency in stealth checks, adds 5 to any rolls they make when attempting to stealth. That means they don’t even have to worry about succeeding on very easy checks.
Then we have Grunak the Killer, a 20th level orc barbarian with proficiency in athletics and a 20 in strength. Grunak will automatically succeed on easy and easier checks, but she’ll also have no problem with hard checks.
Those essentially become her easy. She’ll also be able to grapple against creatures that should be nearly impossible to subdue.
What we don’t see, thanks to bounded accuracy, are situations that are impossible for the Grunaks out there. You never need anything over a +11 bonus to be able to succeed.
Compared to earlier editions when you might see a +20 bonus at 20th level just to keep up with the difficult challenges, this concept allows the rules to be more forgiving. While Grunak is clearly more skilled than Joe, Joe still has a chance of succeeding on hard tasks.
“…we make no assumptions on the DM’s side of the game that the player’s attack and spell accuracy, or their defenses, increase as a result of gaining levels. Instead, we represent the difference in characters of various levels primarily through their hit points, the amount of damage they deal, and the various new abilities they have gained.”Rodney Thompson, Legends and Lore, WotC
There’s really no better way to say it. Because of bounded accuracy, the bonuses we get don’t create such a drastic difference between the ordinary and extraordinary. Instead of relying on huge bonus increases as we level up, we get to see a shift in focus towards what our characters can do.
The abilities we get as we level up now have the ability to focus on being extremely cool, instead of worrying about building up our numbers. Sure, there are plenty of abilities out there that give us an advantage, or provide a bonus here and there, but most just allow you to do something really cool. Bounded accuracy makes this less of a numbers game and more of an RPG.
That leads us really well into combat. Monsters feel the same effects that our player characters do from bounded accuracy. The maximum AC of 30 is a huge thing to discuss. It means that Average Joe can hit most creatures in 5e. There are thousands of creatures throughout 5e, and only about 120 that have an AC of 20 or greater.
Does that mean a peasant can slay a Tarrasque?? No! Of course not. Deadly creatures make up for this change in AC in the same way that our characters do. They have more health and stronger hits, with even more interesting abilities.
The way the game is currently designed means that creatures don’t have to be impossible to hit just to be strong. There are many different ways a creature can provide a deadly encounter.
On the same token, our player characters gain the ability to face higher CR monsters by gaining more health and dealing more damage. They’ll get a bit better at hitting above ACs, but the main goal is to deal more damage, and take more damage.
Magical items often provide bonuses. To keep with the principles of this game’s design, magical items in 5e have no more than a +3 bonus. The ones that do have such a large bonus are typically legendary items or artifacts and don’t just wind up in the hands of your average adventurer.
This gives magical items the opportunity to be something more than a number stick. We see a lot of really interesting abilities come to the forefront as highly powerful since everyone isn’t just running to the sword with the highest bonus.