How D&D Combat Works: A Clear Step-by-Step Guide

26 March 2026

D&D combat intimidates a lot of new players. The terminology is unfamiliar, the turn order seems complicated, and everyone seems to know what they’re doing except you. The reality is simpler than it looks. Here’s how a combat encounter actually works, from start to finish.

The basic structure: rounds and turns

Combat in D&D is divided into rounds. Each round represents approximately 6 seconds of in-game time. Every participant in the fight gets one turn per round.

The order of turns is determined by initiative — a Dexterity check everyone makes at the start of the fight. Highest result goes first, lowest goes last. That order stays the same for the entire fight.

Step by step

1. Determine surprise. The DM checks whether either side caught the other off-guard. Surprised creatures can’t move or act on their first turn.
2. Roll initiative. Everyone rolls a d20 and adds their Dexterity modifier. The DM ranks everyone from highest to lowest.
3. Take turns. Starting with the highest initiative, each creature takes their turn.
4. Repeat. Once everyone has gone, the round ends and a new one begins.

What you can do on your turn

On your turn you have three main resources to spend:

Movement

You can move up to your speed (typically 30 feet for most races). You can split this movement before and after your action — move 10 feet, attack, then move 20 feet.

Moving through difficult terrain (rubble, shallow water, underbrush) costs double movement. Every foot moved costs 2 feet of speed.

Action

Your action is the main thing you do on your turn. The most common options:

Bonus action

Some classes and abilities give you a bonus action — an additional action you can take on top of your main one. Rogues use bonus actions for Cunning Action (Dash, Disengage, or Hide). Two-weapon fighters use a bonus action to make their off-hand attack.

You can only take a bonus action if something specifically says you can. You don’t have a bonus action to spend by default.

Reaction

A reaction is an instant response to a specific trigger. You get one reaction per round, and it can happen on someone else’s turn.

The most common reaction is an opportunity attack: if an enemy moves out of your melee reach without taking the Disengage action, you can immediately make one melee attack against them.

Making an attack roll

When you attack, roll a d20 and add:

• Your relevant ability modifier (Strength for most melee attacks, Dexterity for ranged and finesse weapons)
• Your proficiency bonus (if you’re proficient with the weapon)

If your total equals or exceeds the target’s Armor Class (AC), the attack hits. Then roll damage — the weapon’s damage dice plus your ability modifier.

Critical hits

If you roll a natural 20 on the attack roll (before modifiers), it’s a critical hit. Roll all the damage dice twice and add them together, then add your modifiers once.

Missing

A miss deals no damage. No partial hits, no reduced damage — just a miss.

Hit points and going down

When a creature takes damage, subtract it from their current hit points. At 0 HP, the creature falls unconscious.

When a player character drops to 0 HP, they aren’t dead — not immediately. They start making death saving throws: at the start of each turn, roll a d20.

• 10 or higher = success
• 9 or lower = failure
• Three successes = stable (still unconscious, but no longer dying)
• Three failures = dead

Rolling a natural 1 counts as two failures. Rolling a natural 20 brings you back to 1 HP immediately.

Any damage while at 0 HP counts as a failure. A single attack that deals enough damage to equal your maximum HP kills you outright.

Armor Class

Armor Class is your defence against attacks. It’s determined by what you’re wearing:

• No armour: 10 + Dexterity modifier
• Light armour (leather, studded leather): Armour base + Dexterity modifier
• Medium armour (chain shirt, half plate): Armour base + Dexterity modifier (max +2)
• Heavy armour (chain mail, plate): Fixed armour value, Dexterity doesn’t help
• Shield: +2 to AC, regardless of armour type

Concentration

Some spells require concentration to maintain — the caster must actively sustain the effect. If they take damage while concentrating, they must make a Constitution saving throw (DC = 10, or half the damage taken, whichever is higher) to maintain concentration. Fail, and the spell ends.

You can only concentrate on one spell at a time. Casting a second concentration spell ends the first automatically.

This is why Constitution matters for spellcasters.

Common mistakes in your first combat

Not knowing your action options. Review the list above and pick two or three actions that suit your character. Know those cold.

Forgetting bonus actions. Especially relevant for Rogues and characters using two weapons. Read your class features — you likely have bonus actions you’re not using.

Moving before you’ve thought about your turn. Once you’ve moved, you can’t take it back. Decide what you want to do, then commit your movement last.

Ignoring the environment. Pillars give cover (+2 AC). High ground and flanking positions matter. The terrain is part of the fight.

The short version

Combat is: roll initiative, take turns, spend your action and movement, make attack rolls against Armour Class. Repeat until one side is down. The rules support a lot of creative options, but the core loop is simple. Learn your own actions first and the rest fills in naturally.

The full combat rules, including grappling, mounted combat, underwater fights, and cover mechanics, are in Chapter 9 of the Player’s Handbook. (Affiliate link — we earn a small commission at no cost to you.)