Injury and death are frequent threats in D&D, as detailed in the following rules.
Hit Points represent durability and the will to live. Creatures with more Hit Points are more difficult to kill. Your Hit Point maximum is the number of Hit Points you have when uninjured. Your current Hit Points can be any number from that maximum down to 0, which is the lowest Hit Points can go.
Whenever you take damage, subtract it from your Hit Points. Hit Point loss has no effect on your capabilities until you reach 0 Hit Points.
If you have half your Hit Points or fewer, you’re Bloodied, which has no game effect on its own but which might trigger other game effects.
Resting
Adventurers can’t spend every hour adventuring. They need rest. Any creature can take hour-long Short Rests in the midst of a day and an 8-hour Long Rest to end it. Regaining Hit Points is one of the main benefits of a rest. The rules glossary (see "Rules Definitions") provides the rules for Short and Long Rests.
Each weapon, spell, and damaging monster ability specifies the damage it deals. You roll the damage dice, add any modifiers, and deal the damage to your target. If there’s a penalty to the damage, it’s possible to deal 0 damage but not negative damage.
When attacking with a weapon, you add your ability modifier—the same modifier used for the attack roll—to the damage roll. A spell tells you which dice to roll for damage and whether to add any modifiers. Unless a rule says otherwise, you don’t add your ability modifier to a fixed damage amount that doesn’t use a roll, such as the damage of a Blowgun. See chapter 6 for weapons’ damage dice and chapter 7 for spells’ damage dice.
When you score a Critical Hit, you deal extra 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. If the attack involves other damage dice, such as from the Rogue’s Sneak Attack feature, you also roll those dice twice.
Damage dealt via saving throws uses these rules.
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. For example, when a wizard casts Fireball, the spell’s damage is rolled once for all creatures caught in the blast.
Many saving throw effects deal half damage (round down) to a target when the target succeeds on the saving throw. The halved damage is equal to half the damage that would be dealt on a failed save.
Each instance of damage has a type, like Fire or Slashing. Damage types are listed in "Rules Definitions" and have no rules of their own, but other rules, such as Resistance, rely on damage types.
Some creatures and objects have Resistance or Vulnerability to certain damage types. 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. For example, if you have Resistance to Cold damage, such damage is halved against you, and if you have Vulnerability to Fire damage, such damage is doubled against you.
Multiple instances of Resistance or Vulnerability that affect the same damage type count as only one instance. For example, if you have Resistance to Necrotic damage as well as Resistance to all damage, Necrotic damage is reduced by half against you.
Modifiers to damage are applied in the following order: adjustments such as bonuses, penalties, or multipliers are applied first; Resistance is applied second; and Vulnerability is applied third.
For example, a creature has Resistance to all damage and Vulnerability to Fire damage, and it’s within a magical aura that reduces all damage by 5. If it takes 28 Fire damage, the damage is 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).
Some creatures and objects have Immunity to certain damage types and conditions. Immunity to a damage type means you don’t take damage of that type, and Immunity to a condition means you aren’t affected by it.
Hit Points can be restored by magic, such as the Cure Wounds spell or a Potion of Healing, or by a Short or Long Rest (see "Rules Definitions").
When you receive healing, add the restored Hit Points to your current Hit Points. Your Hit Points can’t exceed your Hit Point maximum, so any Hit Points regained in excess of the maximum are lost. For example, if you receive 8 Hit Points of healing and have 14 Hit Points and a Hit Point maximum of 20, you regain 6 Hit Points, not 8.
When a creature drops to 0 Hit Points, it either dies outright or falls unconscious, as explained below.
Here are the main ways a creature can die instantly.
Monster Death.A monster dies the instant it drops to 0 Hit Points, although a Dungeon Master can ignore this rule for an individual monster and treat it like a character.
Hit Point Maximum of 0. A creature dies if its Hit Point maximum reaches 0. Certain effects drain life energy, reducing a creature’s Hit Point maximum.
Massive Damage. 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. For example, if your character has a Hit Point maximum of 12, currently has 6 Hit Points, and takes 18 damage, the character drops to 0 Hit Points, but 12 damage remains. The character then dies, since 12 equals their Hit Point maximum.
If your character dies, others might find a magical way to revive your character, such as with the Raise Dead spell. Or talk with the DM about making a new character to join the group. The rules glossary (see "Rules Definitions") has more information on being dead.
If you reach 0 Hit Points and don’t die instantly, you have the Unconscious condition (see "Rules Definitions") until you regain any Hit Points, and you now face making Death Saving Throws (see below).
Knocking Out a Creature
When you would reduce a creature to 0 Hit Points with a melee attack, you can instead reduce the creature to 1 Hit Point and give it the Unconscious condition. It then starts a Short Rest, at the end of which that condition ends on it. The condition ends early if the creature regains any Hit Points or if someone takes an action to administer first aid to it, making a successful DC 10 Wisdom (Medicine) check.
Whenever you start your turn with 0 Hit Points, you must make a Death Saving Throw to determine whether you creep closer to death or hang on to life. Unlike other saving throws, this one isn’t tied to an ability score. You’re in the hands of fate now.
Three Successes/Failures. Roll 1d20. If the roll is 10 or higher, you succeed. Otherwise, you fail. A success or failure has no effect by itself. On your third success, you become Stable (see “Stabilizing a Character” below). On your third failure, you die.
The successes and failures don’t need to be consecutive; keep track of both until you collect three of a kind. The number of both is reset to zero when you regain any Hit Points or become Stable.
Rolling a 1 or 20. When you roll a 1 on the d20 for a Death Saving Throw, you suffer two failures. If you roll a 20 on the d20, you regain 1 Hit Point.
Damage at 0 Hit Points. If you take any damage while you have 0 Hit Points, you suffer a Death Saving Throw failure. If the damage is from a Critical Hit, you suffer two failures instead. If the damage equals or exceeds your Hit Point maximum, you die.
You can take the Help action to try to stabilize a creature with 0 Hit Points, which requires a successful DC 10 Wisdom (Medicine) check.
A Stable creature doesn’t make Death Saving Throws even though it has 0 Hit Points, but it still has the Unconscious condition. If the creature takes damage, it stops being Stable and starts making Death Saving Throws again. A Stable creature that isn’t healed regains 1 Hit Point after 1d4 hours.
Some spells and other effects confer Temporary Hit Points, which are a buffer against losing actual Hit Points, as explained below.
If you have Temporary Hit Points and take damage, those points are lost first, and any leftover damage carries over to your Hit Points. For example, if you have 5 Temporary Hit Points and take 7 damage, you lose those points and then lose 2 Hit Points.
Temporary Hit Points last until they’re depleted or you finish a Long Rest (see "Rules Definitions").
Temporary Hit Points can’t be added together. If you have Temporary Hit Points and receive more of them, you decide whether to keep the ones you have or to gain the new ones. For example, if a spell grants you 12 Temporary Hit Points when you already have 10, you can have 12 or 10, not 22.
Temporary Hit Points can’t be added to your Hit Points, healing can’t restore them, and receiving Temporary Hit Points doesn’t count as healing. Because Temporary Hit Points aren’t Hit Points, a creature can be at full Hit Points and receive Temporary Hit Points.
If you have 0 Hit Points, receiving Temporary Hit Points doesn’t restore you to consciousness. Only true healing can save you.