Advantage and Disadvantage in D&D 5e: Probability Guide

Advantage and disadvantage are two of the most important mechanics in Dungeons and Dragons 5th Edition. Introduced as a way to streamline gameplay, they replace the small, stacking numerical bonuses from previous editions with a simple, elegant system. Instead of adding a +2 for this and a +1 for that, the DM can simply grant you advantage to represent a favorable situation or impose disadvantage to reflect a difficult one. This keeps the game moving quickly and makes it easy for players to understand their odds at a glance.

The rule itself is straightforward. When you have advantage on a d20 roll (an attack roll, an ability check, or a saving throw), you roll two twenty sided dice and use the higher result. For example, if you have advantage and roll a 7 and a 16, you use the 16. Conversely, when you have disadvantage, you roll two d20s and must use the lower result. So in the same scenario, if you rolled a 7 and a 16 with disadvantage, you would be forced to use the 7.

Let's imagine a practical example. A rogue is hidden in the shadows, an advantageous position for an attack. When they fire their bow at a goblin, the Dungeon Master says, "You have advantage on the attack." The player rolls two d20s, getting a 5 and a 17. Because of advantage, they take the 17, add their bonuses, and likely hit the goblin. If that same rogue were instead poisoned (a condition that imposes disadvantage), they would have to take the 5, a much less favorable outcome.

A common misconception is that advantage is just like getting a small bonus. The reality is far more powerful and interesting. A standard d20 roll has an average result of 10.5. When you roll with advantage, that average jumps to 13.82. With disadvantage, it plummets to 7.18. This is often simplified by saying advantage gives you a 'virtual' bonus of about +3.3, but that description doesn't tell the whole story.

The true strength of advantage is how it bends probability toward success. It doesn't just increase your average roll, it significantly increases your chance of hitting a target number, especially moderately difficult ones. It smooths out the randomness of the d20, making you more consistent and reliable. The mechanic's effect is most powerful when you need to roll a number in the middle range of the die, like an 11 or 12. A 50 percent chance of success becomes a 75 percent chance with advantage.

To see this in action, let's look at the probability of meeting or exceeding a target number on a d20. For a target of 5, a normal roll gives you an 80% chance, which advantage boosts to 96%. For a more difficult target of 15, your 30% chance with a normal roll jumps to 51% with advantage, turning a likely failure into a probable success. With disadvantage, the odds are grim: that same target of 15 gives you only a 9% chance of success. This shows that advantage is more than just a bonus, it is a complete change in your expected outcome.

Beyond just affecting your average roll, advantage and disadvantage have a dramatic impact on the extreme ends of the d20 spectrum: the natural 20 (a critical hit on an attack) and the natural 1 (a critical failure). Normally, you have a 5% chance of rolling a 20 and a 5% chance of rolling a 1. This simple probability is turned on its head by this core mechanic.

With advantage, your chance of scoring a critical hit nearly doubles, climbing from 5% to 9.75%. This happens because you only need one of your two dice to land on 20. At the same time, your chance of getting a critical failure becomes almost negligible, dropping to a mere 0.25%. A critical failure with advantage requires you to roll two natural 1s simultaneously, an incredibly rare event. This makes characters who can reliably get advantage, like Barbarians or Rogues, much more likely to produce those memorable, high damage moments.

Disadvantage, as you might expect, creates the opposite effect, and it is brutal. Your chance of landing a critical hit falls to just 0.25%, since you would need both dice to land on 20. Meanwhile, your chance of a critical failure balloons to 9.75%. You now have two opportunities to roll that dreaded natural 1, and you must take it if either die shows it. This is a primary reason why imposing disadvantage on a powerful enemy is such an effective tactic: it not only makes them miss more often, but it also makes them more likely to fumble at a crucial moment.

Understanding the power of advantage is one thing, but actively seeking it out is what separates good players from great ones. Gaining advantage should be a primary tactical goal for any adventuring party. The most common sources can be broken down into three categories: positioning, teamwork, and special abilities or spells.

Clever positioning is a martial character's best friend. Attacking a creature that is prone gives you advantage on your melee attack rolls, which is why the Shove action is so useful. Similarly, attacking from an unseen position, such as from being hidden, grants advantage on the attack. For teamwork, the simplest option is the Help action. By using your action, you can distract a foe, giving the next ally who attacks them advantage on their roll. This is perfect for setting up a Rogue's Sneak Attack or ensuring a Paladin's Divine Smite finds its mark.

Finally, many spells and class features are built around this mechanic. Spells like *Faerie Fire* and *Guiding Bolt* explicitly grant advantage against their targets. Some conditions, like being paralyzed from *Hold Person*, are even better, granting automatic critical hits for melee attackers. Class features like the Barbarian's Reckless Attack are a high risk, high reward method of gaining advantage on every attack, while a Samurai Fighter can simply decide to grant themselves advantage for a turn with their Fighting Spirit feature.

Just as you should constantly seek advantage, you must also be vigilant about avoiding disadvantage. Dungeon Masters use disadvantage to represent any number of challenging circumstances, from environmental hazards to debilitating conditions. Recognizing and mitigating these situations is key to your survival.

Many common actions can impose disadvantage. For example, making an attack with a ranged weapon beyond its normal range but within its long range imposes disadvantage. Trying to shoot a bow at a prone target also gives you disadvantage, as they present a smaller profile. Likewise, attacking a creature you cannot see (perhaps they are invisible or in magical darkness) will also give you disadvantage on your attack rolls.

Conditions are another frequent source of disadvantage. Being blinded, frightened, poisoned, or restrained can all impose disadvantage on your attack rolls or ability checks. A few levels of exhaustion will also start applying disadvantage to your rolls. This is also a tool for the DM to use for roleplaying situations. For example, a DM might rule that you have disadvantage on a Charisma (Persuasion) check if you are trying to negotiate while holding a bloody axe, or on a Wisdom (Perception) check in dim light.

One of the best parts of the advantage and disadvantage system is its simplicity, and nowhere is this more apparent than in its stacking rules. The rule is simple: advantage and disadvantage do not stack. If you have multiple sources of advantage, you don't get to roll more dice. You still just roll two d20s and take the higher. For example, if you are hidden and attacking a prone enemy, you have two sources of advantage, but you still only roll two d20s. The same is true for disadvantage.

The most important rule to remember is about cancellation. If you have at least one source of advantage and at least one source of disadvantage, they cancel each other out completely. It doesn't matter if you have five sources of advantage and only one source of disadvantage. They negate each other, and you make a straight roll with a single d20. You do not count them up to see which one has more sources.

This rule has significant tactical implications. Let's say a Barbarian uses their Reckless Attack feature, granting them advantage on their attacks this turn. However, an enemy spellcaster has cast a spell that makes the Barbarian blinded, which imposes disadvantage. The advantage and disadvantage cancel out, and the Barbarian makes a normal attack. This can also be used offensively. If an enemy has a powerful feature that grants them disadvantage (like being in sunlight for a drow), a single, simple Help action from an ally can give them advantage, canceling out their innate penalty and allowing them to attack normally.

The advantage and disadvantage system is the engine that drives tactical combat in 5e. It's designed to promote teamwork and reward players for thinking beyond simply dealing the most damage with their own character. The best parties learn to manipulate what is sometimes called the 'advantage economy,' working together to ensure they have advantage as often as possible while imposing disadvantage on their enemies.

For players, this means communicating and collaborating. The party's Fighter can use the Shove action to knock an enemy prone, setting up the Rogue or Paladin for a devastating, advantage-fueled strike. A Wizard can use a control spell like *Web* to restrain enemies, giving the entire party advantage on their attacks against them. Even the humble Help action is a testament to this design, allowing a character to contribute to a fight's outcome even if their own attacks are not effective.

Dungeon Masters can use these same principles to design memorable and challenging encounters. A small group of kobolds using their Pack Tactics to gain advantage can overwhelm a party that doesn't respect their positioning. An assassin perched in the darkness with advantage on their first attack can create a dramatic and dangerous opening to a battle. By layering in environmental factors, enemy abilities, and conditions, a DM can create a dynamic battlefield where simply standing still and attacking is rarely the best option.