How Concentration Works in Fifth Edition

It's one of the most-forgotten rules at the table, and one of the most punishing when you get it wrong. Here's the whole thing in plain terms — what concentration is, what breaks it, and the saving throw that trips up new spellcasters.

One spell at a time

Some spells have a duration that reads "Concentration, up to 1 minute" (or 10 minutes, or an hour). That tag is the rule: to keep the spell going, you have to concentrate on it — and you can only concentrate on one spell at a time.

Cast a second concentration spell and the first one ends immediately, no choice about it. So Bless and Haste can't both be running from the same caster. This is the single most common mistake newer players make: stacking two concentration buffs and not realising the first silently dropped.

Spells without the tag — Magic Missile, Fireball, Cure Wounds — don't need concentration at all. They happen and they're done. Concentration is only for the ongoing ones.

What breaks it

Four things end your concentration:

• Casting another concentration spell — as above, the new one replaces the old.
• Taking damage — you must make a Constitution saving throw, or the spell drops. This is the big one, covered below.
• Being incapacitated or killed — knocked to 0 HP, stunned, paralysed, or worse: concentration ends.
• Choosing to end it — you can drop it any time, no action required.

The damage save — and its maths

This is the part people get wrong. When you're concentrating and you take damage, you roll a Constitution saving throw to hold on. The DC is:

So a poke of 8 damage is a DC 10 save (half of 8 is 4, which is below 10, so the floor applies). But a big hit of 30 damage is a DC 15 save. The harder you're hit, the harder it is to keep the spell up — which is exactly why concentration spells feel fragile on a squishy caster standing in the open.

You make a separate save for every instance of damage. Get hit by three arrows, that's three saves. War Caster and proficiency in Constitution saves are the classic ways to shore this up.

Why it matters more than it looks

Concentration is the balancing lever for the whole spell list. The reason Hypnotic Pattern, Haste, Spirit Guardians and Bless are as strong as they are is that you can only run one, and any hit threatens it. Forget that, and you're accidentally playing a more powerful — and less fair — version of the game.

The awkward part: tracking it live

The rule is simple to read. What's genuinely hard is remembering it mid-session — that you're concentrating on Bless, that the goblin's crossbow bolt means a save right now, that casting Web would drop the Bless you forgot about two turns ago. Under time pressure, with three other players talking, that's where it slips.