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

26 March 2026

You know the scene: someone says “roll initiative,” the table goes loud, and you’re suddenly supposed to know what you’re allowed to do on your turn while the battle map looks like a traffic jam. Take a breath. Fifth edition combat is mostly a small loop, rounds, turns, and a handful of choices you make on repeat until the fight ends.

Here’s how that loop actually works, in the order you’ll feel it at the table.

Rounds and turns (the frame everything hangs on)

Combat is sliced into rounds. Each round is about 6 seconds in the fiction, and in the rules, every creature in the fight gets one turn per round.

Turn order is initiative: at the start of combat, everyone rolls a d20 and adds Dexterity modifiers (plus any special bonuses). The DM lines people up high to low, and that order repeats every round until someone wins, runs, or surrenders.

The usual start-up sequence

1. Figure out surprise (if any). Surprised creatures can’t move or take an action on their first turn of combat, and they can’t take a reaction until after that turn.
2. Roll initiative. One d20 + Dexterity per creature (unless a rule gives a fixed value).
3. Take turns in order. Highest initiative goes, then the next, until everyone has acted. That finishes the round.
4. Start the next round at the top of the order and do it again.

If you want a tighter tour of initiative quirks, read Initiative in D&D 5e next.

What you actually spend on your turn

Think of your turn as a budget. Most turns you’re juggling movement, an action, and sometimes bonus actions or reactions, but only when a rule gives them to you.

Movement

You can move up to your speed (often 30 feet). You’re allowed to split movement around your action, slide forward, hit something, slide back, unless something says you can’t.

• Difficult terrain costs double: each foot moved uses 2 feet of speed.
• Standing up from prone costs half your speed.
• You’ll sometimes burn movement on other things (crawling costs double, for example).

Action (the big decision)

Your action is your main “I do the thing” moment. Common picks:

Bonus action

You only have a bonus action when something grants one, Cunning Action, certain spells, two-weapon fighting’s extra attack, and so on. If nothing says “as a bonus action,” you don’t have a bonus action waiting. For the full budget on one turn, read action economy explained.

Reaction

You get one reaction per round. It refreshes at the start of your turn.

The poster-child reaction is the opportunity attack: if a hostile creature you can see leaves your reach using its movement, action, or reaction, you can use your reaction to make one melee attack against it, unless something lets it leave safely (like Disengage).

That rule alone is why opportunity attacks and Dash / Disengage matter so much.

Attack rolls, AC, crits, and misses

When you attack, roll a d20 and add:

• The ability modifier the weapon or spell tells you to use for the attack roll (often Strength for melee, Dexterity for finesse/ranged, unless a feature overrides it),
• Your proficiency bonus if you’re proficient with the weapon or the spell uses proficiency.

Meet or beat the target’s Armor Class (AC)? You hit. Roll damage as the weapon/spell says (usually dice + the same ability modifier you used for damage if the rules say so, don’t assume every attack adds the mod to damage without checking).

• Critical hit on a natural 20 on the attack roll: roll all damage dice twice, add modifiers once (unless a rule says otherwise for a given die).
• Miss: you deal no damage. There aren’t “chip damage” defaults in the core rule unless something special grants it.

Hit points, dropping, and death saves

Damage subtracts from current HP. At 0 HP, you’re unconscious (player characters follow the dying rules, not instant “you’re a corpse” unless a rule says so).

Death saving throws (for a PC at 0 HP, at the start of your turns):

• Roll a d20 (this is not a normal saving throw, no ability modifiers unless something explicitly changes that).
• 10+ = one success; 9 or lower = one failure.
• Three successes = you stabilize (0 HP, unconscious, no longer dying).
• Three failures = you die.
• Natural 1 = two failures.
• Natural 20 = you regain 1 HP and wake up.

Other critical bits at 0 HP:

• Damage while at 0 HP usually causes death save failures (a hit from an attacker within 5 feet that’s a critical hit counts as two failures).
• Massive damage can kill outright: if damage leftover after hitting 0 equals or exceeds your HP maximum, you die instantly.

A few rules that show up every campaign

Armor Class is your passive “to-hit” threshold for attack rolls. How you calculate it depends on armor, Dexterity caps with medium armor, shields, special features, cover, and magic. If you want the full spreadsheet of your AC math, read how armor class works.

Concentration matters the instant someone casts bless, hex, web, or banishment: you can only concentrate on one spell at a time; damage forces Constitution saves to hold the spell (DC 10 or half the damage, whichever is higher). Casting another concentration spell ends the first.

Mistakes that quietly cost new players fights

• You plan movement last, then regret it. Decide your goal (“get to the downed ally,” “break line of sight”), then spend movement deliberately.
• You forget the action economy extras your build is built around, bonus actions for rogues and two-weapon fighters, reactions for shield and opportunity control.
• You treat the room like flat golf. Pillars and doors are cover; light and sight lines decide advantage. The environment is part of your kit.

If you only remember one paragraph

Combat is initiative order, repeated each round. On your turn you move, take an action, maybe a bonus action, and you keep a reaction in your pocket until it’s used and resets on your next turn. Attacks are d20 + mods vs AC; saves are d20 + mods vs DC. Everything else is options layered on that spine.

Go deeper: surprise, critical hits, ranged attacks, mounted combat, underwater fights.

The full combat rules, mounted combat, grappling, underwater fights, and the complete equipment tables, live in the Player’s Handbook.