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Probability Calculator
Calculate the probability of single or combined events instantly.
Probability Calculator
Choose a calculation type below.
Probability
0%What is Probability?
Probability measures how likely an event is to occur, expressed as a value between 0 (impossible) and 1 (certain), or as a percentage. This calculator handles single events and combined events (independent).
Probability Formulas
Single Event: P = Favorable Outcomes ÷ Total Outcomes
P(A and B) = P(A) × P(B) — independent events
P(A or B) = P(A) + P(B) − P(A) × P(B)
Frequently Asked Questions
What does "independent events" mean?
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Independent events don't affect each other's outcome — like flipping a coin twice. This calculator assumes independence for the "A and B" and "A or B" calculations.
Can probability be negative or greater than 100%?
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No, probability always falls between 0% and 100% — representing impossible to certain outcomes.
What's a real-world example of "A or B"?
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Finding the probability of drawing a red card OR a face card from a deck — since these events can overlap, the formula subtracts the overlap to avoid double-counting.