How likely you are to have every piece of your combo in hand by a given turn, counting the tutors that can find them.
How this is worked out
Your combo is a set of pieces, and each piece can be filled by one or more cards. The combo counts as assembled when every piece is in your hand, or a tutor you’re holding can fetch it, one tutor for each missing piece. A tutor that puts the card on top of your library counts from your next draw.
Where the maths can be done exactly (no mulligans, and every tutor finds any piece straight to your hand), it is. Otherwise the page plays 200,000 games and counts. It uses a fixed starting point, so the same inputs, and the same link, always give the same figure, and it tells you how far that figure could be from the true one.
Your opening hand is 7 cards and each turn you draw one more. In a pod of three or more players nobody skips their first draw, so by your turn 3 you’ve seen 10 cards. In a duel, the player going first skips it. Your commander starts in the command zone, so it isn’t in your library: that’s 99 cards, or 98 with partners or a background.
This counts whether the cards are in your hand. It doesn’t know whether you have the mana to cast them, or whether an opponent will stop you.