Damage and Critical Hits, Roll It Right

The attack hits. Now every player at the table reaches for different dice, and someone asks the same question as last week: do I double the modifier on a crit? No. Here is the whole of it, in the order it happens, quoted from the System Reference Document 5.2.1.

The damage roll

The SRD puts it in one line: "You roll the damage dice, add any modifiers, and deal the damage to your target."

Three details hide in the paragraph around it.

• Weapons add the same modifier as the attack. "When attacking with a weapon, you add your ability modifier—the same modifier used for the attack roll—to the damage roll." Hit with Strength, add Strength. Stab with a Dagger using Dexterity, add Dexterity.
• Spells tell you. "A spell tells you which dice to roll for damage and whether to add any modifiers." Most add nothing. Read the spell.
• Damage never goes below zero. "If there's a penalty to the damage, it's possible to deal 0 damage but not negative damage."

The weapon table sets the dice. A Dagger deals 1d4 Piercing, a Longsword 1d8 Slashing (1d10 in two hands, its Versatile property), a Greataxe 1d12 Slashing and a Greatsword 2d6 Slashing.

Greataxe or Greatsword?

Both are Heavy, Two-Handed weapons. The averages settle the old argument.

A die averages half of one more than its highest face: a d12 averages 6.5, a d6 averages 3.5, so 2d6 averages 7. The Greatsword wins by half a point a swing, and it swings steadier: two dice bunch toward the middle, so it rolls 7 more often than any other total, while the Greataxe rolls every number from 1 to 12 equally often. The Greataxe costs 30 GP to the Greatsword's 50 GP, and each carries a different mastery property (Cleave against Graze), which can matter more than half a point.

The Critical Hit

A Critical Hit starts on the d20. "If you roll a 20 on the d20 (called a 'natural 20') for an attack roll, the attack hits regardless of any modifiers or the target's AC. This is called a Critical Hit."

Then the damage: "Roll the attack's damage dice twice, add them together, and add any relevant modifiers as normal. For example, if you score a Critical Hit with a Dagger, roll 2d4 for the damage rather than 1d4, and add your relevant ability modifier."

So the dice double and the modifier doesn't. A +3 Greatsword crit is 4d6 + 3, an average of 17, not 20.

Every extra die on the attack doubles too: "If the attack involves other damage dice, such as from the Rogue's Sneak Attack feature, you also roll those dice twice." This is why a Rogue's crit lands so hard. The flat numbers stay flat, and every die in the hit comes twice.

How often? A natural 20 comes up 1 time in 20, 5%. With Advantage you roll two d20s and keep the higher, so you crit unless both dice miss the 20: 1 − (19/20)² = 9.75%, nearly double.

One roll, many targets

"When you create a damaging effect that forces two or more targets to make saving throws against it at the same time, roll the damage once for all the targets." Fireball is the SRD's own example: each creature in the blast makes a Dexterity saving throw, "taking 8d6 Fire damage on a failed save or half as much damage on a successful one". Roll the 8d6 once. Everyone who fails takes that total.

Half is "half the damage that would be dealt on a failed save", rounded down. Roll 27 on the 8d6 and a creature that saves takes 13. On average 8d6 comes to 28, so a save is worth 14 Hit Points.

Resistance, Vulnerability, and the order they go in

"If you have Resistance to a damage type, damage of that type is halved against you (round down). If you have Vulnerability to a damage type, damage of that type is doubled against you." Two Resistances to the same damage never make a quarter: "Multiple instances of Resistance or Vulnerability that affect the same damage type count as only one instance."

When several things change one hit, the order matters. "Adjustments such as bonuses, penalties, or multipliers are applied first; Resistance is applied second; and Vulnerability is applied third."

The SRD's example: a creature with Resistance to all damage and Vulnerability to Fire stands in an aura that reduces all damage by 5. It takes 28 Fire damage: "first reduced by 5 (to 23), then halved for the creature's Resistance (and rounded down to 11), then doubled for its Vulnerability (to 22)." Done the other way round you get a different answer, so follow the order.

Immunity sits above both: "Immunity to a damage type means you don't take damage of that type."

Where the damage goes

"Whenever you take damage, subtract it from your Hit Points." At half your Hit Points or fewer you're Bloodied, which "has no game effect on its own but which might trigger other game effects."

A big enough hit skips the death saves altogether. "When damage reduces a character to 0 Hit Points and damage remains, the character dies if the remainder equals or exceeds their Hit Point maximum." The SRD's example: a maximum of 12, 6 Hit Points left, 18 damage. The character drops to 0 with 12 left over, and 12 equals the maximum, so the character dies. A crit at level 1 can do exactly that.

Monsters skip the whole question: "A monster dies the instant it drops to 0 Hit Points."

At the table

• Roll attack and damage together. If the d20 shows a natural 20, pick up the damage dice and roll them again.
• Say the damage type with the number: "fourteen, fire". Resistance needs it.
• For a save effect, roll once, then call "fail takes 27, save takes 13".

Our 3D roller throws every die in the set, and our app applies the damage to any character in the party. The Book of Dice explains notation like 4d6 + 3 in its Dice Notation Guide, in Part III, The Rolling. All the rules above are in the SRD 5.2.1.

This work includes material from the System Reference Document 5.2.1 ("SRD 5.2.1") by Wizards of the Coast LLC, available at dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License.