D&D Combat Rules: Full Breakdown

Dungeons & Dragons combat operates on a structured turn-based system that governs everything from sword swings to dragon breath. The rules span Chapter 9 of the Player's Handbook (5th Edition) and are the single most rule-dense area of the game — the place where forgetting one clause can flip the outcome of an entire encounter. This page covers the full mechanical architecture of D&D combat: how initiative works, what a turn contains, how attacks resolve, and where the rules get genuinely tricky.

Definition and scope

Combat in D&D 5th Edition is a formalized procedure for resolving conflict between characters and creatures. When the fiction gets hostile — a rogue draws a blade, a spell flies, a monster charges — the game shifts into what the Player's Handbook calls "initiative order," and normal narrative time freezes into discrete rounds, each lasting 6 seconds of in-world time.

That 6-second figure is easy to overlook, but it does real structural work. A fighter attacking twice and a wizard casting a fireball are both happening inside the same 6-second window, which is why the rules treat actions as happening "on your turn" rather than sequentially in literal time. The round is a fiction that makes the game solvable.

The scope of combat rules covers three nested units: the round (one full cycle through all combatants), the turn (a single creature's slice of the round), and the action (the discrete choice made during a turn). Everything else — bonus actions, reactions, movement — branches off this framework. For a broader look at how this fits into the game's full rule architecture, the key dimensions and scopes of D&D page maps the relationship between combat, exploration, and social interaction.

How it works

Combat follows a consistent procedure every round. In order:

1. Determine surprise. The Dungeon Master decides if any side is surprised, typically based on Dexterity (Stealth) checks contested by Wisdom (Perception). A surprised creature cannot move or take actions on its first turn.
2. Establish positions. Combatants are placed — on a grid or in theater-of-the-mind — and distances are tracked.
3. Roll initiative. Each participant rolls a d20 and adds their Dexterity modifier. Ties are broken by comparing Dexterity scores, or by the DM's discretion.
4. Take turns in initiative order. Highest result goes first, descending through the list.
5. Begin the next round. After everyone has acted, the round ends and the cycle repeats until combat is resolved.

On each turn, a creature has one action, one bonus action (if a feature grants it), movement up to its speed, one reaction (which can occur on any turn, not just its own), and the option to interact with one object for free.

The attack roll is the most frequent resolution mechanic. A player rolls a d20, adds their attack modifier (typically proficiency bonus plus the relevant ability modifier — Strength for melee, Dexterity for ranged), and compares it to the target's Armor Class. Meet or beat the AC, and the attack hits. On a hit, damage dice are rolled separately. A natural 20 on the d20 is a critical hit, which doubles all damage dice rolled — not the total, just the dice.

The how it works page covers dice mechanics and probability at a more granular level if the math behind attack rolls and saving throws is the main interest.

Common scenarios

Opportunity attacks catch players off-guard constantly. When a creature moves out of an enemy's reach, that enemy can use its reaction to make one melee attack. The trigger is leaving reach — not turning around, not being distracted. Creatures can avoid this by using the Disengage action, which costs their full action.

Concentration spells introduce a parallel resource management layer. A caster maintaining hold person or bless must make a Constitution saving throw any time they take damage — DC 10 or half the damage taken, whichever is higher. Failing drops the spell. This is why enemies with multiple attacks are disproportionately dangerous to spellcasters, even at lower damage values.

Two-weapon fighting is a common point of confusion. Wielding a light melee weapon in each hand lets a creature attack with the off-hand weapon as a bonus action — but that bonus action attack does not add the ability modifier to damage unless the character has the Two-Weapon Fighting style. The penalty is subtle but meaningful at higher levels.

Decision boundaries

The deepest mechanical debates in D&D combat cluster around two distinctions: action versus bonus action, and movement before versus after action.

A bonus action is not a second action. Only features that explicitly use the words "as a bonus action" grant a bonus action — the Cunning Action feature of a Rogue (available starting at level 2) lets them Dash, Disengage, or Hide as a bonus action, but a Fighter without a similar feature cannot. The D&D frequently asked questions page covers this specific question in detail, because it generates more table arguments than almost any other rule.

Movement, by contrast, can be split around an action. A creature with 30 feet of speed can move 10 feet, attack, then move the remaining 20 feet. This matters enormously for positioning — it turns the action sequence into a spatial puzzle rather than a fixed sequence.

The contrast worth internalizing: actions are singular and exclusive (only one per turn, with rare exceptions like the Action Surge feature of the Fighter class), while movement is a pool that can be distributed freely across the turn. Getting that distinction wrong is the fastest way to either underpower a character or accidentally build illegal turns that a DM will eventually catch. The how to get help for D&D page outlines where rules disputes can be researched and adjudicated using official sources.