Boy or Girl Paradox Calculator
Probability both children are boys under different conditions: at least one boy, older is a boy, or a boy born on a given weekday.
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Probability both children are boys under different conditions: at least one boy, older is a boy, or a boy born on a given weekday.
Boy or Girl Paradox Estimator
Enter your numbers below for an instant estimate.
How It Works
Key concepts behind this calculator
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Read the breakdown and the explanation.
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Boy Quick Guide
Typical values for reference.
| Condition | Cases | Both boys | Probability |
|---|---|---|---|
| No information | 4 | 1 | 25% |
| At least one boy | 3 | 1 | 33.3% |
| Older child is a boy | 2 | 1 | 50% |
| Boy born on Tuesday | 27 | 13 | 48.1% |
| Rule of Thumb | Check inputs | Use as a guide | Round sensibly |
Boy or Girl Calculator FAQ
Answers to common questions about this calculator.
1/3 if you only know at least one is a boy; 1/2 if you know the older is.
It makes a second boy more likely to fit the description.
Count the equally likely outcomes that match the condition.
It is an estimate based on the inputs you enter. Check real quotes, labels or official guidance for important decisions.