DnD Action Types: Action, Bonus Action, and Reaction
Every round of combat in Dungeons & Dragons runs on a strict economy of action types — and knowing how to spend them is one of the most consequential skills a player develops. The three core types are the Action, the Bonus Action, and the Reaction, each governed by specific rules in the 5th Edition Player's Handbook. Misreading which type a spell or ability requires is one of the most common sources of table disputes, particularly at levels where characters start stacking multiple abilities.
Definition and scope
A combat turn in D&D 5e gives each creature exactly 1 Action, up to 1 Bonus Action (if something grants it), and up to 1 Reaction (which refreshes at the start of each of that creature's turns). These are not interchangeable slots — an Action cannot be spent as a Bonus Action, and a Bonus Action cannot substitute for a full Action. The Player's Handbook (Chapter 9) is explicit on this point.
Action: The primary resource of a turn. Attacking, casting most spells, Dashing, Disengaging, Dodging, Helping, Hiding, and using most activated item features all cost an Action.
Bonus Action: A supplementary action available only when a specific rule, feature, or spell grants it. A Fighter with no Bonus Action sources has nothing to spend in that slot. Common sources include the Two-Weapon Fighting rule, the Cunning Action feature for Rogues (available at level 2), and spells with a casting time of "1 bonus action."
Reaction: A single response that triggers on a specific event, usually outside the creature's own turn. The most cited example is the Shield spell, which triggers when the caster is hit by an attack. Opportunity Attacks also use a Reaction — which is why burning a Reaction on Shield early in a round can leave a character exposed to a flanking enemy.
For a broader picture of how combat fits into the game's structure, the key dimensions and scopes of DnD page maps the full framework.
How it works
The action economy operates in sequence within a single turn, but Reactions can interrupt the normal flow entirely — triggering on another creature's turn, mid-movement, or even mid-resolution of a spell.
A few structural points from the Player's Handbook that trip up even experienced players:
- Bonus Actions are conditional, not automatic. If no class feature, spell, or item grants a Bonus Action, the slot simply doesn't exist for that character on that turn.
- Casting time determines action type. A spell with "casting time: 1 action" costs an Action. A spell with "casting time: 1 bonus action" costs a Bonus Action. The two are not interchangeable, and the PHB (p. 202) includes an important restriction: when a Bonus Action spell is cast, the only other spell castable that turn is a cantrip with a casting time of 1 action.
- Reactions have declared triggers. The PHB lists specific conditions that activate each Reaction ability. A player cannot hold a Reaction "in reserve" for an unspecified event — the trigger must match exactly.
- The Ready action converts an Action into a deferred Reaction. A creature can use its Action to Ready a spell or attack, specifying a trigger. If that trigger occurs before the creature's next turn, the readied action fires as a Reaction. Critically, a readied spell still expends the spell slot even if the trigger never occurs (PHB Chapter 9, "Ready").
Common scenarios
Two-Weapon Fighting is the single most frequently misapplied Bonus Action rule. When a character attacks with a light melee weapon in the Action and holds a second light weapon, the PHB (p. 195) permits a Bonus Action attack with the off-hand weapon — but the ability modifier is not added to the damage roll (unless the character has the Two-Weapon Fighting fighting style).
Cunning Action (Rogue, level 2) allows Hiding, Dashing, or Disengaging as a Bonus Action — dramatically changing how Rogues move through combat and apply Sneak Attack.
Opportunity Attacks are the Reaction most players encounter first. When a hostile creature moves out of a character's reach without Disengaging, that character can expend a Reaction to make one melee attack. Spending that Reaction earlier — on Shield, for instance, or the Counterspell spell — eliminates the option for the rest of the round.
Misty Step (2nd-level conjuration) is a Bonus Action teleport of up to 30 feet. Players new to spellcasting sometimes cast it alongside another leveled spell in the same turn — which the PHB explicitly prohibits under the Bonus Action casting restriction noted above.
Decision boundaries
The practical question at the table is always sequencing: which resource to spend, and when. Three decision points matter most.
Hold the Reaction or spend it? The Reaction refreshes at the start of each turn, but it only refreshes once. Spending it on an Opportunity Attack early in a round is a valid trade — but losing Counterspell availability against a high-level caster later in the same round can be catastrophic. The answer depends on threat assessment, not instinct.
Action vs. Bonus Action spell pairing. Because the PHB's Bonus Action spell rule restricts other spells to cantrips, a Sorcerer deciding between casting Misty Step (Bonus Action) plus Fire Bolt (cantrip Action) versus Fireball (Action) alone is making a genuine strategic choice — not a bookkeeping question.
When to Ready instead of act. Readying converts a resource into a conditional deferred effect, which costs both the Action and the Reaction. That's a significant double spend. The DnD frequently asked questions page covers common Ready action disputes that arise from this cost.
Understanding how it works at the system level makes these in-combat decisions faster, cleaner, and considerably less likely to derail a session into a rulebook archaeology expedition.