Probability
Arkham Horror Dice Roll Probabilities
This is the home page for dice probabilities for dice roll skill checks, modifiers and their combinations.
- Normal (only a 5 or 6 die roll result is a success)
- Blessed (only a 4, 5 or 6 die roll result is a success)
- Cursed (only a 6 die roll result is a success)
- Shotgun (6 die roll results are 2 successes)
- Bonus Skills (add 1 to each die roll): Dodge, Grapple, Hide, Library Use, Psychology, Spot Hidden from Dunwich Horror
- One's Re-roll Skills (re-roll all die results of 1): Camouflage, Linguistics, Listen, Persuade, Run, Wrestle from Kingsport Horror
- Dice Re-roll Skills: Bravery, Expert Occultist, Marksman, Stealth plus various spells like Foresee
- Dice Re-roll Ability of Mandy Thompson
The tables are long and include odds of all permutations of the above skill modifiers for 1 - 20 dice and 1 - 5 minimum successes.
Accuracy should be quite good. The calculations were made using a combinatorics algorithm and tested by comparing the results to those made by a brute force calculation that rolled all possible dice combinations and counted each success. The latter method is limited due to time constraints -- checking all these combinations for 20 dice would likely take several thousand years! All brute force permutations were verified to be identical to their combinatorics counterparts for 1 to 4 dice (the Mandy/Bonus/One's Re-roll combo is a real hog) and some of the simpler combinations were verified for up to 5, 10 and 13 dice.
Tables have been organized into the following sets for easy lookup and analysis.
Table Sets and Downloads
- Combos by Successes table -- definitions and how to's
- Combos by Skill Modifier table -- definitions and how to's [TBD]
- Dice Rolls Probabilities download (pdf)
