D&D Combat Rules: Initiative, Actions, and Turns

Combat in Dungeons & Dragons 5th Edition runs on a precise mechanical clock — initiative determines who acts when, and a layered action economy dictates what each creature can actually do in 6 seconds of fictional time. This page covers the complete structure of D&D 5e combat rounds, from rolling initiative to resolving a full turn, including the tradeoffs that make tactical decisions matter and the misconceptions that regularly slow down tables.

Definition and scope

A combat round in D&D 5e represents approximately 6 seconds of in-world time, per the Player's Handbook (PHB, Chapter 9). Every participant in an encounter — player characters, monsters, and NPCs — takes exactly one turn per round, and turns are ordered by initiative. The full cycle of every combatant taking one turn constitutes a round.

The scope of combat rules as defined in 5e covers three nested structures: the encounter (the whole fight), the round (one complete cycle of turns), and the turn (one creature's allocated slice of action within a round). Each creature's turn is itself subdivided into movement, one action, one possible bonus action, and one possible reaction — four distinct mechanical categories that interact in specific, rules-defined ways.

The combat rules in the D&D 5e System Reference Document 5.1 (SRD), published by Wizards of the Coast under Creative Commons Attribution 4.0, are the authoritative public reference for these mechanics.

Core mechanics or structure

Initiative is determined at the start of combat, before any turns occur. Each participant rolls 1d20 and adds their Dexterity modifier. The Dungeon Master rolls once for each group of identical monsters, or separately for each monster at their discretion. Ties between player characters and monsters are resolved in favor of the player characters in many tables, though the PHB technically allows a contested Dexterity check or a coin flip — both are valid.

The initiative order is fixed at the start of combat and does not change each round unless a specific rule intervenes (such as the Alert feat, which grants a +5 bonus to initiative and prevents surprised creatures from gaining advantage against the feat-holder).

Each turn contains a specific set of resources:

Surprise is a special condition applied at the start of combat, not a separate phase. A surprised creature cannot move, take actions, or take reactions on its first turn. Surprise does not grant an extra round — it simply denies a creature its first turn's options.

Causal relationships or drivers

Initiative order creates action economy asymmetry. A party of 4 player characters taking turns before a solo monster effectively delivers 4 attacks before the monster can respond. This is why CR (Challenge Rating) calibration in the Dungeon Master's Guide accounts for monster Multiattack and legendary actions — mechanical tools designed to partially offset the structural disadvantage of a solo creature in a turn-order system.

The 6-second round length is a design constraint that shapes every action's weight. A Dash action doubling movement speed means a character can cover 60 feet in one turn — roughly the width of a large room. Ranged spellcasters who position at 90 feet are genuinely out of charge range for most melee enemies on any given turn, which is not arbitrary feel but geometric consequence of movement math.

The Dexterity modifier's dual role — governing both initiative and AC (when wearing no armor or light armor) — creates a feedback loop that makes Dexterity-heavy builds structurally advantaged in combat initiation and survivability simultaneously. This is a deliberate 5e design choice compared to earlier editions, where initiative had more varied calculation methods.

Classification boundaries

Not every action in the fiction is an action in the mechanical sense. This distinction causes more mid-session arguments than almost any other rule. Specific classifications:

The boundary between action and bonus action is binary and non-negotiable in RAW (Rules As Written): a bonus action cannot be used as an action and vice versa. A Rogue's Cunning Action lets them Dash, Disengage, or Hide as a bonus action — that does not free up their action to do so a second time.

Tradeoffs and tensions

The Dodge action is mechanically powerful (attackers have disadvantage on all attacks against the dodging creature, and the creature has advantage on Dexterity saving throws) but sacrifices offensive output entirely. For a Fighter with 3 attacks per turn, choosing Dodge represents an enormous opportunity cost. For a Wizard with a concentration spell already running, Dodge is often the correct choice — a raised eyebrow at players who forget this.

Ready introduces a time-value problem: the readied action fires as a reaction, meaning the creature loses its reaction for any other purpose (like an opportunity attack) until the trigger fires or the creature's next turn arrives. Players frequently Ready actions without calculating the reaction cost.

The combat rules overview on this site explores encounter pacing in more depth, but within the turn structure, action surge (Fighter class feature) is the clearest example of intended tension: the ability to take a second action once per short rest dramatically shifts the Fighter's turn-economy but is exhausted after a single use, creating a decision point about when to commit it.

Bonus action spells interact with action spells in a way that generates constant confusion: the PHB rule at §Bonus Action specifies that when a bonus action is used to cast a spell, the only spell castable with an action that same turn must be a cantrip with a casting time of 1 action. This is not a case where players must choose one or the other — it's a restriction on which action-slot spell can follow a bonus action spell. The spell slots and spellcasting reference covers the full interaction.

Common misconceptions

"Bonus actions are optional free actions." Incorrect. Bonus actions are a specific resource that only exists when granted by a class feature, spell, or rule. A character with no bonus action source has nothing to spend, not a flexible extra action.

"You roll initiative every round." Incorrect. Initiative is rolled once per combat encounter. The order is fixed. Some tables house-rule re-rolling each round; that is homebrew, not RAW.

"Surprise gives you an extra turn." Incorrect. Surprise prevents a creature from acting on its first turn — it does not grant extra turns to the non-surprised party. The surprised creature still occupies its place in the initiative order; it simply cannot act when that slot arrives.

"Reactions happen immediately before the triggering action." Partially incorrect. Reactions occur in response to a trigger, but the precise timing depends on the reaction. An opportunity attack occurs when a creature leaves a threatened space — not when it declares movement. The Shield spell triggers when the caster is hit by an attack — after the attack roll succeeds, before damage is applied.

"Dashing lets you attack." Incorrect. Dash doubles movement speed for the turn — it does not grant an attack. It uses the creature's action, replacing any attack that action would have produced.

Checklist or steps (non-advisory)

Standard Combat Turn Sequence — 5e RAW

  1. Start of turn: any ongoing effects that trigger "at the start of your turn" resolve (e.g., regeneration, burning, lingering effects on certain spells)
  2. Move up to full speed — can be divided before, between, or after other turn actions
  3. Take one action (Attack, Cast a Spell, Dash, Disengage, Dodge, Help, Hide, Ready, Search, Use an Object, or class/race-specific actions)
  4. Take one bonus action if a qualifying rule grants one this turn
  5. End of turn: any ongoing effects that trigger "at the end of your turn" resolve (e.g., certain poison saves, concentration checks if damage was taken mid-turn)
  6. Reaction remains available until used or until the start of the creature's next turn — it is not a turn step but a persistent resource; track it separately

Reference table or matrix

D&D 5e Combat Action Types — Quick Reference

Action Type Cost Can Be Taken Key Examples
Action 1 per turn Always Attack, Cast a Spell, Dash, Disengage, Dodge, Help, Hide, Ready
Bonus Action 1 per turn Only when granted by a rule Cunning Action (Rogue), off-hand attack, certain spells
Reaction 1 per round When trigger occurs Opportunity attack, Shield spell, Counterspell, Readied action
Movement Up to speed Always Walk, climb, swim, crawl (at varying costs per foot)
Free Object Interaction 1 per turn Always Draw/sheathe weapon, open unlocked door, pick up item
Second Object Interaction Costs Action When second needed Drink a potion (second item), close a door after entering

Initiative Roll Modifiers — Common Sources

Source Modifier Type
Dexterity modifier +DEX Ability modifier
Alert feat +5 Flat bonus; also negates advantage from surprise
Jack of All Trades (Bard 2) +half proficiency bonus Applies to all ability checks including initiative
Bless spell +1d4 Concentration spell buff to attack rolls and saving throws — does not apply to initiative
War Caster feat No bonus Common misconception — does not affect initiative
Portent (Divination Wizard) Replace roll Divination Wizard can substitute a Portent die result for initiative

References