Free Probability Calculator - Calculate Event Probability
Calculate probability for single and multiple events. Best free probability calculator 2025 - AND, OR, conditional probability made easy.
Quick Answer
Probability = favorable outcomes / total possible outcomes. P(A) ranges from 0 (impossible) to 1 (certain). P(A AND B) = P(A) × P(B) for independent events. P(A OR B) = P(A) + P(B) - P(A AND B). Example: coin flip heads = 1/2 = 0.5 = 50%. Calculate at practicalwebtools.com.
Key Facts about Probability Calculator:
- Probability ranges from 0 (impossible) to 1 (certain)
- P = favorable outcomes / total outcomes
- P(A AND B) = P(A) × P(B) for independent events
- P(A OR B) = P(A) + P(B) - P(A AND B)
- Complementary: P(not A) = 1 - P(A)
- All probabilities in a sample space sum to 1
- Conditional: P(A|B) = P(A AND B) / P(B)
Why Use Our Probability Calculator?
Probability calculations:
Single Event
Calculate basic probability.
Combined Events
AND and OR probability.
Conditional
P(A given B) calculations.
Complement
P(not A) automatically.
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Get probability immediately.
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How to Probability Calculator in 3 Easy Steps
Calculate probability:
Enter Events
Define favorable and total outcomes.
Choose Type
Single, AND, OR, or conditional.
Get Probability
View result as fraction, decimal, %.
Master Probability
Calculate any probability scenario
Combine events easily
Multiple output formats
Essential for statistics
Common Use Cases for Probability Calculator
Essential for:
Frequently Asked Questions
Everything you need to know about our probability calculator
How do I calculate probability?
Favorable / total outcomes. Die rolling 6: 1/6 = 16.7%.
P = favorable outcomes / total outcomes. For rolling a 6 on a die: 1 favorable (6) / 6 total = 1/6 ≈ 0.167 = 16.7%.
What is P(A AND B)?
P(A) × P(B) for independent events. Two heads: 0.5 × 0.5 = 0.25.
Probability of both A and B occurring. For independent events: P(A AND B) = P(A) × P(B). Two coin flips both heads: 0.5 × 0.5 = 0.25.
What is P(A OR B)?
P(A) + P(B) - P(A AND B) to avoid double counting.
Probability of A or B or both occurring. P(A OR B) = P(A) + P(B) - P(A AND B). Removes double counting.
What is conditional probability?
P(A given B) = P(A AND B) / P(B).
P(A|B) is probability of A given B has occurred. P(A|B) = P(A AND B) / P(B). It is probability of A when we know B is true.
Still have questions? Try the tool yourself!
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