Sourcemined
Slay the Spire 2
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Verified on build 23811903

Card reward odds calculator

Rare cards get likelier every time a reward doesn't give you one, then the chance resets. Tell the calculator how long it's been and see exactly what your next reward can hold, down to a single card.

Character
Reward from
Regular fight: 3 cards
Cards since your last rare
Count every card you were offered in fight rewards since the last rare one (0 at the start of a run). The rare chance gains 1 point per card and caps after 45.

Next card reward

First card (later cards shift as the offset moves):

  • Rare0%
  • Uncommon35%
  • Common65%
At least one rare
0%
Rares on average
0.00
Cards until a rare
≈ 15.2
Rarity offset
−5%
Non-rares upgraded
0%
Rare chance for the next card, by cards since the last rare
  1. 0 cards: 0%
  2. 3 cards: 1%
  3. 6 cards: 4%
  4. 9 cards: 7%
  5. 12 cards: 10%
  6. 15 cards: 13%
  7. 18 cards: 16%
  8. 21 cards: 19%
  9. 24 cards: 22%
  10. 27 cards: 25%
  11. 30 cards: 28%
  12. 33 cards: 31%
  13. 36 cards: 34%
  14. 39 cards: 37%
  15. 42 cards: 40%
  16. 45 cards: 43%

Assumes every card is unlocked and a single-player run. How it's worked out is on the methodology page.

How card rewards roll

Each card in a reward rolls its rarity separately. The game takes the listed chance for the fight type and adds a hidden rarity offset: it starts at −5%, grows by one point for every card that isn't rare (half a point at Ascension 7), stops at +40%, and drops back to −5% as soon as a rare shows up. That's why the first fights of a run almost never offer a rare, and a long dry spell makes one close to certain.

Once the rarity is set, the card is picked evenly from your character's cards of that rarity, skipping cards already in the reward. With every card unlocked each character has 20 commons, 35 uncommons and 25 rares, so any one rare shows up in a regular reward about 0.79% of the time over a run.

Card rarity chances by fight type
RewardListed rareFirst card rare, after a rare1+ rare, after a rare1+ rare, run average
Regular fight3%0%0%19.7%
Elite fight10%5%17%30.9%
Boss100%100%100%100%

The run average assumes every reward comes from a regular fight (or every one from an elite) and lets the offset settle; it takes 45 cards in a row without a rare to reach the cap. The full rules, with what's verified, are on the methodology page.