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Commander Deck Formula: Counts and Draw Probability

Build a Commander deck count and calculate simple draw probabilities, separating Magic card roles from the unrelated construction Deck Calculator.

By Uddhav Gopani, FounderPublished 25 September 2026Reviewed 29 September 2026

Commander Deck Formula: Counts and Draw Probability

Start with the card-game meaning of deck

In Magic: The Gathering, Commander deck construction concerns cards, mana and game plans. A construction Deck Calculator estimates physical decking materials and has no useful connection to this question. The official Commander format page describes the usual arrangement as one commander plus a 99-card library, with singleton restrictions and basic-land exceptions. Special card text and alternative commander arrangements can change the details, so verify the legality of the actual list. The mathematical examples below use one commander outside a shuffled library containing exactly 99 cards.

Make the card count add up

An illustrative planning list might contain 37 lands, 10 mana-acceleration cards, 10 card-advantage cards, 10 interaction cards and 32 other cards. These groups sum to 99, and adding the commander gives 100. The numbers are bookkeeping choices, not a universal recommended recipe or a guarantee of a balanced deck. A low-cost strategy and a strategy built around expensive spells can need different resources. Begin with the strategy and then use the count to reveal what you have allocated, rather than treating a category total as a rule of the format.

Prevent double counting of flexible cards

A card may provide both mana and card selection, but it still occupies one physical slot. For the total deck count, assign each card to one primary category. You can maintain additional tags for its secondary functions without adding those tags to the 99-card total. If ten cards each have two useful roles, that does not create ten additional deck slots. A useful worksheet therefore has one unique card row, one count column and several optional role columns. The count column answers deck size; the tags answer what the deck can do.

Calculate a single-draw probability

With 37 lands in a 99-card library, the probability that one uniformly random draw is a land is 37/99, approximately 37.3737%. The Probability Calculator can check this simple favorable-outcomes-over-total-outcomes calculation using 37 favorable outcomes and 99 total outcomes. That percentage applies to the stated library composition before the draw. If a land is removed and no cards are replaced, the next draw has 36 lands among 98 cards. The draws are dependent because the composition changes. Reusing 37/99 for every later draw ignores that change.

Use combinations for an opening hand

For a seven-card opening hand drawn without replacement, the probability of exactly k lands is C(37,k)×C(62,7−k)/C(99,7), where C(n,r) counts unordered selections. Under these assumptions, the probability of at least two lands is about 81.4177%. This is a hypergeometric calculation, not seven independent repetitions of the same draw. The simple Probability Calculator does not accept a deck list or directly perform this multi-card calculation. The displayed figure is derived from the combination formula, with no mulligan, draw-order or card-specific effects included.

Measure access to a particular role

Suppose ten distinct cards in the library count as access to a desired effect. The chance of seeing at least one in the first seven cards is 1−C(89,7)/C(99,7), approximately 53.7163%. The complement is easier to calculate: all seven cards miss the ten desired cards. This number changes if some of the ten cards cannot perform their role without another card, additional mana or a later turn. It measures drawing a listed card, not successfully resolving a spell or executing a strategy through an opponent's interaction.

Use the numbers to evaluate actual games

Record which assumptions a probability uses: library size, target count, cards seen, replacement policy and any mulligan rule. Compare that model with hands from ordinary play and note whether the counted cards perform the intended jobs. A card that technically produces mana but is rarely usable on time may need a different role label in the next review. Legality, mana curve and the social expectations of the play group remain separate questions. The useful formula is the one attached to a clearly defined draw event, while the deck's overall plan requires more than a percentage.

Use the Probability Calculator

Open Probability Calculator

Source and scope

Wizards of the Coast: Commander format rules