MTG Manabase Calculator

Tell it the turn you want to cast the spell and how many colored pips it costs, and this works out the minimum number of sources you need to do it reliably. It computes the probability directly rather than reading off a table, so you can change the deck size, the consistency you want, and whether you are on the play.

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What this actually computes

A manabase question is a drawing-without-replacement question, which means the hypergeometric distribution answers it exactly. There is no simulation and no estimate here: given a deck size, a number of cards seen, and a number of sources, the probability of holding enough of them is a closed-form calculation.

So this page works the other way round. You say how reliable you want to be, and it finds the smallest number of sources that gets you there.

The formula

P(at least k sources) = 1 − Σ C(S, i) × C(N − S, n − i) ÷ C(N, n)

Where N is the deck size, S the sources, n the cards seen by that turn, and k the pips you need. On the play you have seen 7 + (turn − 1) cards; on the draw, one more.

What the numbers come out at

A 60 card deck, on the play, aiming for 90 percent:

Cast on turnOne pip (C)Two pips (CC)Three pips (CCC)
1162735
2152432
3132229
4122026
5111824
6101722

The second pip is where decks break

Look along any row. Going from one pip to two is not a small step: on turn 2 it moves from 15 sources to 24, which is 60 percent more of your deck committed to a single colour.

That is the real reason two colour decks with double-pip costs are hard to build. Twenty four sources of one colour in a sixty card deck leaves very little room for the other colour, and the moment both halves want CC on turn 2 the arithmetic simply refuses. Either the mana gets greedy and the deck stumbles, or one of the two colours becomes a splash.

Three pips on turn 3 wants 29 sources, which is close to half the deck. That is why CCC costs almost always live in decks that are effectively mono-coloured, whatever the second colour on the card might suggest.

Why Commander is a different game

A 99 card deck changes the answer completely. A single pip on turn 1 needs around 27 sources rather than 16, because your opening seven is a much thinner slice of a much bigger deck.

This is worth knowing before importing a 60 card intuition into Commander. It is not that Commander manabases are built by different rules; it is that the same rules, applied to a deck nearly twice the size, give very different answers.

Where these numbers sit against the published tables

If you have seen Frank Karsten's colored-source tables, which are the reference most deckbuilders work from, you will notice these figures run a card or two higher. That is a difference of assumption rather than of arithmetic.

His tables allow for mulliganing to find your colours, which effectively gives you more looks at the deck and therefore lets you run fewer sources. This calculator assumes you keep your opening seven, which is the more conservative reading and the one that describes the game where you did not want to mulligan.

Neither is wrong, and his work is the reason anybody thinks about manabases numerically at all. If you want to model the mulligan itself, the opening hand calculator handles the London mulligan properly, and that is genuinely a different question: chasing one specific card is not the same problem as building a manabase that supports a whole curve.

What counts as a source

Anything that reliably produces that colour when you need it. Basic lands, dual lands, fetch lands that can find one, and mana creatures or rocks that will already be in play by the turn in question.

A dual land counts for both of its colours, which is exactly why they are valuable rather than merely convenient: one card doing two jobs is the only way the arithmetic above ever comes out in favour of a two colour deck. Lands that enter tapped still count, but not for the turn they arrive, so shade your estimate down slightly if your manabase leans on them.

Frequently asked questions

How many sources do I need for a one-pip spell?

In a 60 card deck, casting it on turn 1 on the play reliably takes about 16 sources for a 90 percent success rate. By turn 3 you have seen two more cards, so 13 will do, and by turn 6 it drops to 10. The later you need it, the more forgiving the manabase.

Why is a double-pip cost so much harder?

Because you need two of the same thing rather than one, and the probability of that falls away sharply. On turn 2 in a 60 card deck, one pip needs about 15 sources and two pips needs about 24, which is over half again as many. This is the single biggest constraint on two color decks.

Do these numbers match Frank Karsten's tables?

They are computed the same way but land a card or two apart, because the assumptions differ. His widely cited tables allow for mulliganing to find your colors, which effectively gives you more looks. This calculator assumes a single keep, which is the more conservative reading, and it says so on every result.

What counts as a source?

Anything that can produce that color when you need it: basic lands, dual lands, fetch lands that find one, and mana creatures or rocks that are already in play. A dual land counts as a source for both of its colors, which is exactly why dual lands are valuable rather than merely convenient.

Why does Commander need so many more sources?

Because your opening seven is a much smaller slice of a 99 card deck. A single pip on turn 1 needs around 27 sources in Commander against 16 in a 60 card deck. The deck is bigger, so each individual card is less likely to be the one you need.

What consistency should I aim for?

Ninety percent is the usual target, meaning you cast the spell on curve nine games in ten. Pushing to 95 percent costs several more sources, and for a card you are happy to cast a turn late, 85 percent is often the better trade. The right answer depends on how much the spell matters to your plan.

Does being on the play or the draw change it?

Yes, by one card, and that one card is worth roughly one source. On the draw you have seen an extra card by any given turn, so you can run slightly fewer sources. This calculator defaults to on the play, which is the harder case.

Does this account for mulligans?

No, deliberately. It assumes you keep your opening seven, which makes it the conservative figure. If you want to model mulligans, the opening hand calculator handles the London mulligan properly, and chasing a specific card that way is a different question from building a manabase.

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