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Both calculators run independently — change the inputs on either side to compare results.

Birthday Paradox Calculator

Find the surprisingly high probability that at least two people in a group share a birthday. Use it to demonstrate why coincidences are far more likely than intuition suggests.

Number of People (people)

Days in Year (days)

Fill in the required fields to see your result.

Probability

Combinations and Permutations Calculator

Calculate combinations (nCr) and permutations (nPr), with or without replacement, for counting and probability problems. Use it for lottery odds, team selection, and combinatorics assignments.

Total Items (n) (items)

Items Selected (r) (items)

Calculation Type

With Replacement

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Key differences

	Birthday Paradox Calculator	Combinations and Permutations Calculator
Category	Probability	Probability
Inputs required	2	4
Result	Probability of Match	Result (ways)
What it does	Find the surprisingly high probability that at least two people in a group share a birthday. Use it to demonstrate why coincidences are far more likely than intuition suggests.	Calculate combinations (nCr) and permutations (nPr), with or without replacement, for counting and probability problems. Use it for lottery odds, team selection, and combinatorics assignments.