Exact model
Avoid a natural 1 critical failure on a d20 attack roll
- Probability:
- 95%
- Odds:
- 19 to 1
- dBan
- +12.8 dBan
Nineteen of the fair d20’s 20 results avoid the natural 1 that the 2024 D&D Basic Rules treat as an automatic miss on an attack roll.
Calculation
p = 19 results other than natural 1 / 20 results = 19/20
Assumptions
The d20 is fair and rolled once for an attack. Avoiding a natural 1 does not guarantee that the attack succeeds. Modifiers, rerolls, advantage, and disadvantage are excluded. Other checks or role-playing systems can follow different rules.