Combine age

Combine age is the sum of all the ages in a group. E.g. if two friends are 15 years old together they have 30 years. If 5 friends have 20 years then all together then they can celebrate 100 years. On this unique calculator you can find the exact date of your combine birthday.

If a group of seven friends meet, then they will find a celebration for every day of the year! For seven people you can find 448 celebrations a year!!!
Its because there are many variations and combine birthday (CB) are more often than once a year like a normal birthday is.

For example, two people celebrate CB twice a year. Its because combine age of two people is running double the speed than normal. If baby twins are born on January 1, after 6 months (July 1) they will have their 1st combine birthday and in one year's time, they will have already 2nd CB.
Its similar for 3 or more people. Age of 3 people are running 3 times faster.

For 7 people in the group, you can find combine birthdays for two, three... to seven. There are many variations

The following explanation is for math fun :) To find how many CB there can be for a group of 7, its a nice example of combination their order of selection does not matter. More about how to calculate combination, you can find here.
How many couples is posible to make from group of 7? Its 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 2-3, 2-4, 2-5, 2-6, 2-7, 3-4, 3-5, 3-6, 3-7, 4-5, 4-6, 4-7, 5-6, 5-7, 6-7. All together 21 combinations.

Combine Birthday	1	2	3	4	5	6	7
Combination from a group of 7	1 of 7	2 of 7	3 of 7	4 of 7	5 of 7	6 of 7	7 of 7
Number of combinations	7	21	35	35	21	7	1
Celebration per year	1	2	3	4	5	6	7
Total CB celebration per year	7	42	105	140	105	42	7
All celebrations per year	448

Legend
Combine Birthday - how many people are included in the calculation
Combination from group of 7 - for how many of people from group of 7 is calculation
Number of combinations - e.g. 21 see equation above
Celebration per year - e.g. 2, because 2 people celebrate CB twice a year
Total CB celebration per year - Number of combinations times number of celebration per year, e.g. 21x2=42
All celebrations per year - All total CB together. It means, that in group of a 7 people, there are 448 different celebrations!
Its more than once per day. Let's celebrate!