Same birthday probability Calculator

Calculates the probability that one or more pairs in a group have the same birthday.

Same birthday probability
    1. persons
    2. in a group

    1. Probability with same birthdays
    2. %
(1) the probability that all birthdays of n persons are different.

(2) the probability that one or more pairs have the same birthday.

This calculation ignores the existence of leap years.
Same birthday probability
[1-2] /2Disp-Num
[1]  2017/12/05 06:36   Female / 40 years old level / Others / A little /
Purpose of use
Settling an argument.
In a random sample of "n" people, 2 are found to share the same birthday.
In a second random sample of people, 2 are found to share the same birthday.
What are the odds that both pairs of people share the same birthday?
[2]  2009/07/30 02:00   Male / More than 60 / Others / Very /
Purpose of use
Very useful for backing up a bet taken in a pub. Thank you - I won.
I love this kind of "dispute" settler - in addition, the formulae are beautifully complex in appearance, so my non-maths friends are entirely bamboozled.


Thank you for your questionnaire.
Sending completion


To improve this 'Same birthday probability Calculator', please fill in questionnaire.
Male or Female ?
Male Female
Under 20 years old 20 years old level 30 years old level
40 years old level 50 years old level 60 years old level or over
Elementary school/ Junior high-school student
High-school/ University/ Grad student A homemaker An office worker / A public employee
Self-employed people An engineer A teacher / A researcher
A retired person Others
Very Useful A little Not at All
Purpose of use?
Comment/Request (Click here to report a bug).Bug report (Click here to report questionnaire.)
Calculation bug(Please enter information such as specific input values, calculation result, correct result, and reference materials (URL and documents).)
Text bug(Please enter information such as wrong and correct texts)
Your feedback and comments may be posted as customer voice.