Probability Calculator
Compute single-event, combined, and conditional probabilities, plus dice and coin presets.
Set the scenario
Updates as you typeMode
What are you computing? ?
Live formula
P(A) = favorable / total
Inputs
Favorable outcomes ?
3
Total outcomes ?
10
Inputs
P(A) ?
50%
P(B) ?
30%
Inputs
P(A ∩ B) ?
15%
P(B) ?
30%
Preset
Pick an experiment ?
Number of dice
2
Sides per die ?
Target sum
7
Number of flips
10
Display (format)
Show result as
Formula
Single event:
favorable outcomes
total outcomes
=
P(A)
Complement:
P(not A)
=
1
−
P(A)
Independent (AND):
P(A ∩ B)
=
P(A)
×
P(B)
Union (OR):
P(A ∪ B)
=
P(A)
+
P(B)
−
P(A ∩ B)
Conditional:
P(A | B)
=
P(A ∩ B)
P(B)
- P(A)
- Probability that event A occurs (between 0 and 1).
- P(not A)
- Probability that A does NOT occur — the complement.
- P(A ∩ B)
- Probability that both A and B occur (intersection).
- P(A ∪ B)
- Probability that A or B (or both) occur (union).
- P(A | B)
- Probability of A given that B has occurred.
- Odds
- Ratio of favorable to unfavorable, expressed as p : (1 − p).
Independent means the outcome of A does not affect B. If they are dependent, use the conditional rule: P(A ∩ B) = P(A) × P(B | A). Probabilities are always between 0 (impossible) and 1 (certain).