Calculating the likelihood of a single event is easy. But what happens when you need to know the probability of three, four, or five events happening at the same time?
Whether you are a student solving a statistics problem, a trader assessing market risks, or a sports bettor building a parlay, the math gets complicated quickly. Our Multi-Event Probability Calculator does the heavy lifting for you. Unlike standard tools that assume everything is random, this calculator features a unique Correlation Toggle to simulate real-world scenarios where one event influences another.
Probability Calculator
How to Use the Multi-Event Probability Calculator
This tool is designed to answer the question: “What is the chance that ALL of these things happen?”
- Add Your Events: Click “Add Event” to create as many variables as you need.
- Enter Probabilities (%): Input the percentage chance of each individual event occurring.
- Tip: If you only have Betting Odds (e.g., 2.50), use our Implied Probability Calculator first to convert them into percentages.
- The Correlation Toggle (Advanced):
- OFF (Independent): Use this for unconnected events (e.g., a Coin Flip AND a Roulette Spin). The calculator simply multiplies the probabilities.
- ON (Correlated): Use this for related events (e.g., “Lakers to Win” AND “LeBron to score 20+ points”). Use the slider to estimate how strongly the events are linked.
- Analyze the Result: The tool calculates the probability that ALL occur, NONE occur, or AT LEAST ONE occurs.
Related Tools: If you are strictly looking to calculate the payout of a sports betting accumulator based on odds, use our Parlay Calculator. To determine if the probability you found offers value against the bookie, check the True Odds Generator.
Understanding the difference between these two modes is critical for accurate math.
Example 1: The Independent Parlay (Random)
You want to know the odds of three specific things happening that have no relation to each other:
- Flipping “Heads” on a coin (50%).
- Rolling a “6” on a die (16.6%).
- Drawing a Heart from a deck of cards (25%).
Calculation: Since the coin doesn’t care about the dice, these are independent. The chance of all three happening is approx 2.08%.
You bet on an NFL game:
- Kansas City Chiefs to Win (60%).
- Patrick Mahomes to throw 2+ Touchdowns (60%).
If you calculate this as independent (0.60 × 0.60), you get 36%. This is wrong.
If Mahomes throws 2 TDs, the Chiefs are much more likely to win. These events are positively correlated. Using the Correlation Toggle, you will see the true probability is closer to 50-55%, which explains why Bookmakers give lower odds on SGPs than standard parlays.
Frequently Asked Questions (FAQ)
What is the formula for independent events?
For independent events, the formula for all events occurring is simply the product of their individual probabilities: P(A and B) = P(A) × P(B).
How do I calculate “At Least One” occurring?
The easiest way is to calculate the chance that none of them happen, and subtract that from 100%. The formula is: 1 – (Chance of None).
Why does correlation increase probability?
If events are positively correlated, the success of one makes the success of the other more likely. In a “Perfect Correlation” scenario (100%), if Event A happens, Event B is guaranteed to happen. Therefore, the combined probability is simply equal to the lowest individual probability, rather than the product of both.