Probability Calculator
Calculate basic, combined, and conditional probabilities step by step.
1 · Basic Probability — P(A) = favourable / total
2 · Combined Events — P(A), P(B) → P(A and B), P(A or B)
3 · Conditional Probability — P(A|B) = P(A∩B) / P(B)
4 · Dice & Coins
What is a Probability Calculator?
A probability calculator helps you quantify the likelihood of events expressed as a value between 0 (impossible) and 1 (certain), often also shown as a percentage or a fraction. Probability is the foundation of statistics, data science, gambling, risk management, and everyday decision making. This tool covers the four most common probability computations: simple probability from counts, combined probability for two events, conditional probability (what's the chance of A given B has happened), and dice or coin flip probabilities.
All results include the formula used and a plain-English explanation so you can understand — not just copy — the answer. Everything runs in your browser; no data is sent to any server.
How to Use
- Section 1 — Basic: Enter the number of favourable outcomes and total outcomes, then click Calculate.
- Section 2 — Combined: Enter P(A) and P(B) as decimals (0–1), choose the relationship, then click Calculate.
- Section 3 — Conditional: Enter P(A∩B) and P(B) to find P(A given B).
- Section 4 — Dice & Coins: Select a die, choose the target value, and optionally set the number of rolls to find the probability of at least one hit.