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Birthday Problem Probability Calculator
x402
Birthday Problem Probability Calculator is a paid API for AI agents from probability-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).
Calculates birthday problem probabilities: chance any two people in a group share a birthday, chance someone shares your birthday, and group sizes needed for 50% or 99% probability thresholds.
Price / call$0.02
Success—
StatusUnknown
How this service works
Birthday problem: chance two people in a group share a birthday, chance someone shares yours, group size for 50 or 99 percent.
Output
Returns a JSON object containing: probability that at least one pair shares a birthday, probability that no one shares a birthday, probability that someone shares your specific birthday, the expected number of shared pairs, and the minimum group sizes needed to reach 50% and 99% chance of any shared birthday, plus the group size needed for a 50% chance someone shares your birthday. Also includes metadata fields like source, asOf, and any disclaimers.
Example use cases
Classroom birthday paradox demo
“I'm teaching a class of 28 students and want to know the probability that at least two of them share a birthday — can you run the birthday problem calculation for a group of 28?”
Party planning birthday odds check
“I'm throwing a party with 50 people. What's the chance that at least two guests share a birthday, and what are the odds someone shares my specific birthday?”
Finding the 50% threshold for birthday match
“How many people need to be in a room before there's at least a 50% chance that two of them share a birthday? Also give me the number for a 99% chance.”
Technical details
Endpoint
GEThttps://probability-calc.x402tookit.com/birthday-problem?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need precise birthday problem probability computations — especially the classic paradox scenario (chance any pair shares a birthday), the personalized variant (chance someone shares YOUR birthday), or the threshold group sizes for 50%/99% confidence. Prefer this over a general statistics API when the birthday problem is the specific question, as it returns all relevant variants in a single call with clean structured output.
Side effects
- Missing required 'people' query parameter returns an error
- People value outside range 1–100000 may return an error or unexpected result
- Non-integer values for 'people' or 'days' may be rejected
- Very large group sizes may produce probabilities indistinguishable from 1.0
- Payment failure returns HTTP 402 before computation occurs
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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