Three or more people having the same birthday. i am trying to determine the probability of three people having the same birthday when chosen from a group of "n" people. i have calculated that in a group of 23 people, the probability is greater than 50 per cent that at least 2 of those people will have the same birthday (and the calculations are here: ) i know the number of people required is 88 for 3 people, 187 for 4, 313 for 5, etc. (the link for that information is ~fcale/ccc/dc. pdf) anyway, when i use the attached formula, it becomes inaccurate when the number of people required is 6 or greater. does anyone know if there is a better equation (or method) to use when calculating this?