Probability Tree Generator
Describe It, Get a Tree
Describe your scenario and get a free probability tree generator online — every branch calculated and validated.
See It in Action
From a natural-language prompt to a finished probability tree — then refine it with another message.
Key Features
Everything you need to go from a probability question to a finished, validated probability tree.
Describe the scenario in natural language and get a complete probability tree in seconds — no modeling skills required.
A responsive tree layout recalculates every node position as the tree grows, so branches never overlap or crowd.
Path probabilities are computed for you, and every branch group is checked so sibling probabilities always sum to 1.
Keep talking to your tree: adjust the scenario, add stages, or ask questions about the probabilities it shows.
Fine-tune labels and probabilities right on the canvas.
Export crisp PNG, PDF, or SVG files from this online probability tree maker — ready for homework, slides, or reports.
Feature Tour
Describe It, Get a Tree
Ask in natural language — coin flips, medical tests, marbles in a bag — and get a complete probability tree with every branch probability computed. It's the fastest way to create a probability tree diagram online without manual layout.
Refine It by Chat
Follow up in natural language: make the coin biased, add a third draw, or change the scenario. The tree updates while the conversation keeps context.
Edit Nodes & Branches Inline
Click any node or branch to adjust labels and probabilities right on the canvas — downstream results recalculate instantly.
Export for Anywhere
Download your tree as PNG, PDF, or SVG, or copy it as an image straight into homework, slides, or notes.
How to Make a Probability Tree
From scenario to shareable diagram — no drawing, no manual math.
Describe the Scenario
AI Generates & Calculates
Refine by Chat or by Hand
Export & Share
Use Cases
What People Draw with It
Real prompts from teachers, students, and analysts — each one becomes a complete probability tree in seconds.
Flip a fair coin three times — I showed my students every path to exactly two heads on one canvas.
Math Teacher, Lincoln High School
A test is 95% accurate. My students finally saw why a positive result isn't the whole story.
Statistics Lecturer, State University
Two draws from a bag of 3 red and 2 blue marbles, no replacement — my son's homework was sorted in seconds.
Parent, Homework Helper
Launch on time, delay, or pivot — I mapped the whole decision tree before the board meeting.
Product Manager, SaaS Startup
Our point guard shoots 78% from the line. The tree made both-free-throws odds obvious to the whole team.
Sports Analyst, Varsity Stats Club
40% chance of rain each day this weekend — one tree later, the picnic decision made itself.
Weekend Planner, Outdoor Club
Probability 101
What Is a Probability Tree Diagram?
The simplest way to reason about conditional probability — one branch at a time. ProbPath’s probability tree maker is built and reviewed by educators and data scientists.
A probability tree diagram is a visual map of a multi-stage random process: each node is an event, each branch is a possible outcome labeled with its probability, and each path from root to leaf is one complete sequence of outcomes. You can create a probability tree diagram online with ProbPath to avoid manual layout and arithmetic.
Nodes and Branches
Every node is an event; every branch leaving it is one possible outcome, labeled with its probability. The branches leaving the same node always add up to 1.
Reading a Path
Follow the branches from left to right to read a sequence of outcomes. Multiply along a path to get its probability; add paths together to combine scenarios.
Independent vs. Dependent Events
Coin flips keep the same probabilities at every stage. Drawing marbles without replacement changes them — the tree handles both, and ProbPath recalculates dependent branches for you.
The Math
Probability Tree Formulas, Worked Through
The probability tree diagram generator does the math for you — here is exactly what it computes.
The Multiplication Rule
P(A ∩ B) = P(A) × P(B|A)
Multiply along a path of branches to get the probability of that exact sequence of outcomes. This is the core calculation any probability tree generator performs.
The Addition Rule
P(A or B) = P(A) + P(B)
Add the probabilities of separate paths to find the chance that any of them happens — like 'at least one head in two flips'.
Bayes' Theorem
P(A|B) = P(B|A) · P(A) / P(B)
Flip the conditional — from 'positive test given sick' to 'sick given positive test'. The tree keeps both directions visible.
Worked Example: The Medical Test
A test is positive for 95% of people with a condition and for 5% of people without it. 1% of the population has the condition. You test positive — what is the chance you actually have it? This classic example is often used by Khan Academy and university statistics courses to teach Bayes’ theorem with a probability tree diagram.
| Path | Calculation | Probability |
|---|---|---|
| Sick → Positive | 0.01 × 0.95 | 0.0095 |
| Sick → Negative | 0.01 × 0.05 | 0.0005 |
| Healthy → Positive | 0.99 × 0.05 | 0.0495 |
| Healthy → Negative | 0.99 × 0.95 | 0.9405 |
All four paths sum to exactly 1 — the same check ProbPath runs on every tree it generates.
P(sick | positive) = 0.0095 ÷ (0.0095 + 0.0495) ≈ 16%. A positive result still leaves an 84% chance you don't have the condition — the insight the tree makes obvious.
Build Your First Probability Tree in Seconds
Describe your scenario — the probability tree diagram maker draws, calculates, and validates it.
Frequently Asked Questions
Everything else you might want to know about this probability tree maker and diagram generator.
- Is this probability tree generator free?
Is this probability tree generator free?
Yes — ProbPath is a free probability tree diagram maker to start. You can create and edit probability tree diagrams online without paying. Sign up for a free account to save your chats and come back to them anytime.
- Do I need to install anything?
Do I need to install anything?
No. ProbPath is an online probability tree maker that runs entirely in your browser — there is nothing to download or install. Type a scenario and the tree appears in seconds.
- Can I edit the tree after it's generated?
Can I edit the tree after it's generated?
Yes, two ways. Follow up in natural language — 'make the coin biased' or 'add a third draw' — or click any node or branch on the canvas to edit labels and probabilities directly. Everything downstream recalculates instantly, making it a flexible probability tree creator for homework, slides, and reports.
- Does it check my probabilities?
Does it check my probabilities?
Yes. Every branch group is validated so sibling probabilities sum to exactly 1, and all path probabilities are computed automatically — no manual multiplication, no arithmetic slips.
- Can it handle conditional probability and draws without replacement?
Can it handle conditional probability and draws without replacement?
Yes. Describe dependent events — like drawing two marbles from a bag without replacement — and this probability tree generator updates the conditional probabilities at every stage of the tree.
- Can I ask questions about my tree?
Can I ask questions about my tree?
Yes. Ask things like 'what's the probability of exactly two heads?' or 'which path is most likely?' and get an answer based on the tree on your canvas.
- What formats can I export?
What formats can I export?
PNG, PDF, and SVG — crisp enough for homework, lecture slides, and reports.
- Which languages can I use?
Which languages can I use?
ProbPath understands natural-language descriptions — write your scenario in whatever language you're most comfortable with.