Probability Calculator

To find the likelihood of an event occurring, enter the values in the probability calculator.

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Probability Calculator

Probability calculator finds the possibility of an event occurring from a number of events. The tool uses the probability formula containing the number of outcomes and the times the event occurs.

The result includes the chance of an event taking place and of its not taking place. Values are represented in both decimals and percentages.

What is probability?

The probability of anything means the odds or chance of it taking place. The value of the probability varies between 0 to 1. If it is 1, this means the event will certainly occur while 0 means there is no chance of the event happening.

It is just an idea and not an actual value. 

Probability formula

The probability of A is written as P(A). The formula used to find the probability is:

probability formula

To understand the number of events and outcomes take an example. A bag has 10 balls out of which 3 are pink, and 7 are red.

The outcomes are the total number of balls i.e. 10. To find the possibility of a pink ball being drawn, the number of events is 3. To find the probability of a red ball, its value is 7

The complement of probability tells the chances of it NOT occurring. It has a simple formula. Since the sum of all probabilities must be 1;

p(A’) = 1 - p(A)

How to find the probability and its complement?

You can find the possibility of an event occurring and its complement yourself but we recommend using the probability checker.


To find the probability of a single event, you have to count the total number of every event and add them. Then divide the number of times the required event occurred with the previously calculated value.

Probability Example:

If you draw one card from a deck of playing cards, what is the possibility it will be a 7?


Now, the data we need is:

The number of events =? 

The number of outcomes =?

Since there are 52 cards in a deck this means total outcomes are 52. And as each deck contains a total of 4 number 7 cards, the number of times the event happens is 4. Hence,

n(E) = 4

n(T) = 52

Now using the formula.

p(7) = 4/52

p(7) = 0.077 

Hence this is the answer. Use the percentage calculator to convert it into a percentage.

Probability Complement

By finding the probability complement you can have an idea of what is the likelihood the incident will not happen. Its value can be a sum of probabilities of multiple events or represent a single event as well.


There are 5 colored spice jars. Two jars contain sugar, two contain salt and one jar contains paprika. What are the chances that if you open the first jar, it will be salt?


Step 1: Identification of values.

Outcomes = 2 + 2 + 1

Event = 2

Step 2: Calculation of probability.

P(S) = ⅖

P(S) = 0.4 or 40 percent 

Step 3: Finding complement.

P(S’) = 1 - 0.4

P(S’) = 0.6 or 60 percent 

This means there is a 40 percent chance it is salt and a 60 percent chance that the first jar does NOT contain salt. 

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