DnD Concentration Rules

Concentration is one of the most consequential mechanics in fifth-edition Dungeons & Dragons — a single rule that shapes spell selection, tactical movement, and party composition in every session. It caps how many sustained magical effects a caster can maintain at once, forces meaningful trade-offs, and creates one of the game's most reliable sources of drama: the monster that goes straight for the wizard. This page covers the full definition, the step-by-step mechanism, common edge cases, and the decision points that trip up even experienced tables.

Definition and scope

Concentration is a condition attached to certain spells — identified in the spell's Duration line with the word "Concentration" — that requires the caster to maintain active mental focus for the effect to persist. The rule appears in the Player's Handbook (5th edition, p. 203) and applies to a large portion of the game's most powerful sustained spells: Hold Person, Bless, Banishment, Conjure Animals, Wall of Fire, and roughly 100 others across official sourcebooks.

The scope is deliberately narrow: only spells with "Concentration" in their Duration entry are governed by this rule. Instant-effect spells (Fireball, Cure Wounds), spells with fixed non-concentration durations (Mage Armor at 8 hours), and non-spell abilities are entirely unaffected. That distinction matters more than it might seem — a Paladin's Divine Smite will never compete with a Wizard's Hypnotic Pattern for the same mental slot.

How it works

The mechanics break into four discrete steps:

1. Casting the spell. A caster begins concentration the moment a concentration spell is cast. Any previously maintained concentration spell ends immediately — there is no overlap, no transition period, no "finishing" the old effect first.
2. Maintaining concentration. No action is required to maintain concentration between turns. The caster simply continues to hold focus, which persists until the spell's maximum duration expires, the caster ends it voluntarily (no action required), the caster falls unconscious, or concentration is broken by damage.
3. Taking damage. When a concentrating caster takes damage from any source, a Constitution saving throw is required. The DC equals 10 or half the damage taken, whichever is higher (Player's Handbook 5e, p. 203). A caster who takes 22 points of fire damage must beat a DC of 11 (half of 22, rounded down). A caster who takes 6 points must still beat DC 10.
4. Breaking concentration. Failing the saving throw ends the spell immediately. The effect does not linger, does not wind down — it simply stops. A banished enemy returns to the battlefield on the same turn their captor fails a Con save.

The War Caster feat and the Resilience (Constitution) feat both exist specifically to shore up this vulnerability, which tells you something about how central the mechanic is to character optimization decisions. For a broader look at how these mechanical systems interact, the key dimensions and scopes of DnD page covers the structural layers of the game's rules architecture.

Common scenarios

Multiple conditions on one target. A Wizard casts Hold Person (concentration) on an enemy. A Cleric then casts Bless (also concentration) on allies. These coexist without issue — different casters maintain separate concentration pools. The conflict only arises within a single caster's focus.

Casting a second concentration spell. A Druid maintaining Entangle decides to cast Conjure Woodland Beings. Entangle ends the instant the second spell is cast, regardless of how tactically inconvenient that timing is. Tables sometimes house-rule this, but the RAW (Rules As Written) position from the Player's Handbook is unambiguous.

Incapacitation and sleep. Falling unconscious — whether from dropping to 0 hit points or the Sleep spell — breaks concentration automatically, with no saving throw. The caster does not get a chance to hold the spell together.

Verbal and somatic components while concentrating. Concentration does not prevent a caster from performing other actions, casting non-concentration spells, moving, or using items. The common misconception that maintaining concentration demands the caster's full attention each turn is not supported by the rules as written. The how it works reference covers component requirements in more detail.

Decision boundaries

The sharpest decision point at any table is which concentration spell to hold. A Cleric running Spirit Guardians deals consistent area damage across multiple turns; dropping it to cast Hold Person on a single high-value target is often a net loss against multiple enemies and a net gain in a boss fight. The math is genuinely context-dependent, which is part of what makes concentration spells interesting rather than just powerful.

A second boundary concerns positioning. Any DM who understands concentration will direct enemy movement toward the concentrating caster. A Ranger holding Hunter's Mark in melee is a different risk proposition than a Wizard holding Hypnotic Pattern from 60 feet back. Constitution modifiers, armor class, and available cover all factor into how exposed that concentration save becomes.

The third boundary is the feat investment question. War Caster grants advantage on concentration saving throws and costs a feat slot. Resilience (Constitution) adds a proficiency bonus to Con saves outright. At a Constitution modifier of +1 and proficiency bonus of +3, a proficient Con save sits at +4 — meaning a DC 10 save requires a roll of 6 or higher, roughly a 75% success rate without advantage. Whether that's sufficient depends entirely on how frequently the campaign features enemies capable of landing concentrated fire on a single target.

The DnD frequently asked questions page addresses edge cases that come up repeatedly at tables — including what happens when a spell description conflicts with the core concentration rule in the Player's Handbook.