In Commander, does damage dealt by your commander add up across multiple combats for the 21-damage rule?

The Commander damage rule (sometimes called 'commander damage' or the '21-damage rule') states that if a single commander has dealt 21 or more combat damage to a player over the course of the game, that player loses the game. This total is tracked cumulatively — it never resets.

Crucially, the damage accumulates regardless of how many separate combats, turns, or trips to the command zone the commander has made. Even if your commander dies and is recast three times, all combat damage it dealt before and after counts toward the 21-damage threshold against each opponent. This is defined in the Commander format rules (a supplemental rule to the Comprehensive Rules, specifically referenced in CR 903.10).

Note that only combat damage counts. Damage dealt by your commander through spells, abilities, or triggered effects does NOT count toward the 21-damage total. Only damage dealt while the commander is attacking or blocking applies.

Also note that the 21-damage total is tracked per commander, per opponent. Each player has their own separate damage total against each opposing commander. So if two opponents' commanders have each dealt you 15 combat damage, you are not at 30 — you are at 15 from each, and neither has reached 21 yet.

Example: Your Ur-Dragon commander attacks and deals 9 combat damage to an opponent in turn 5. It dies and you recast it. On turn 9 it deals 7 more damage, then on turn 12 it deals 5 more in a second combat phase. That opponent has now taken 9 + 7 + 5 = 21 commander damage and immediately loses the game.