Single Event Probability
Find the chance of an event by comparing favorable outcomes with the total number of possible outcomes.
Free Online Statistics Tool
Probability Calculator
Calculate the probability of single events, complementary events, independent events, either event, conditional events, and repeated trials.
Calculate Probability
Select a calculation type and enter the required values.
Single Event Probability
Calculate probability using favorable outcomes and total possible outcomes.
Complementary Probability
Calculate the probability that an event will not happen.
Probability of A and B
Calculate the probability that two independent events both occur.
Probability of A or B
Calculate the probability that event A, event B, or both occur.
Conditional Probability
Calculate the probability of event A occurring when event B has occurred.
Repeated Independent Trials
Calculate the probability of at least one success across repeated trials.
Calculator Features
Calculate Different Types of Probability
This tool provides several calculation modes for common probability questions in mathematics, statistics, education, and everyday situations.
Multiple Events
Calculate the chance that two events both occur or that at least one of two events occurs.
Conditional Probability
Measure the probability of an event when another related event is already known to have occurred.
What Is a Probability Calculator?
A probability calculator is an online mathematical tool that determines how likely an event is to occur. Probability values range from 0 to 1. A probability of 0 means the event is impossible, while a probability of 1 means the event is certain.
Probability can also be displayed as a percentage. For example, a decimal probability of 0.75 is equal to 75%. This calculator automatically displays results in decimal, percentage, fraction, and odds formats where applicable.
Common Probability Formulas
Single Event
P(A) = Favorable outcomes ÷ Total outcomes
Complementary Event
P(not A) = 1 − P(A)
Independent Events
P(A and B) = P(A) × P(B)
Either Event
P(A or B) = P(A) + P(B) − P(A and B)
Conditional Probability
P(A|B) = P(A and B) ÷ P(B)
At Least One Success
P = 1 − (1 − p)ⁿ
Simple Instructions
How to Use the Probability Calculator
Follow these steps to calculate probability accurately.
Select a Probability Type
Choose single event, complement, A and B, A or B, conditional probability, or repeated trials.
Enter Your Values
Provide the requested outcomes or probability values. Decimal probabilities must remain between 0 and 1.
Calculate the Result
Select the calculate button to view the probability, percentage, fraction, odds, and formula used.
Helpful Answers
Probability Calculator FAQs
Answers to frequently asked questions about probability calculations.
The basic probability formula is the number of favorable
outcomes divided by the total number of possible outcomes.
The result must be between 0 and 1.
Multiply the decimal probability by 100. For example,
0.45 multiplied by 100 equals a probability of 45%.
A probability of 0.5 means that an event has a 50% chance
of occurring. The event is equally likely to happen or not happen.
Complementary probability is the chance that an event does
not occur. It is calculated by subtracting the event probability
from 1.
For independent events that must both occur, multiply their
probabilities. For either event occurring, add their probabilities
and subtract the probability that both occur.
No. A valid probability cannot be less than 0 or greater
than 1. In percentage form, it must remain between 0% and 100%.
Conditional probability measures the chance of one event
occurring when another event has already occurred. It is
commonly written as P(A|B).