Tested, and working. Here are some enhancements.
As written above, the formula results can be used to sort and group the birthdays by month and sort by day within each month. The year of birth is ignored. Here is the top (fist 20 dates) of my test table. Column A was numbered to enable returning to the original order. Column B contains 120 randomly generated date of birth values. These are Date and Time values (with the time part set to 00:00:00 as they would be if the dates were entered manually). Column C is the key column in sorting. D, E and F show some possibilities in displaying the data.
The first line below shows the original suggested formula for producing a column of data that can be sorted by birthday (month, then day) without regard to year. The second line adds the year to the string, resulting in lines sharing the same birthday being sorted from oldest to youngest.
C2: =RIGHT("00"&MONTH(B2),2)&" "&RIGHT("00"&DAY(B2),2)
C2: =RIGHT("00"&MONTH(B2),2)&" "&RIGHT("00"&DAY(B2),2)&" "&YEAR(B2)
Column C is used only for sorting, and may be hidden if you do not want to display the dates in this manner.
Sorted on column C:
Column D shows one way of redisplaying the results using the name of the month, rather than its number. It also adds the age of the person on this birthday. Sorting on this column will give similar results to sorting on column C (with the second formula), except that those sharing a birth month and day will be sorted from youngest to oldest.
D2: =RIGHT("00"&MONTH(B2),2)&" "&RIGHT("00"&DAY(B2),2)&" "&MONTHNAME(MONTH(B2))&" "&DAY(B2)&" "&YEAR(TODAY())-YEAR(B2)&"yrs"
D2a: =RIGHT("00"&MONTH(B2),2)&" "&RIGHT("00"&DAY(B2),2)&" "&YEAR(TODAY())-YEAR(B2)&"yrs"
D2a produces the same result as C2, with the age in years on the birthday in the current year appended.
Sorted on column D:
Column E displays only the month and day values for the birthday. The formula is a subset of the formula in column D. This column will correctly group the birthdays into months and sort the groups by day of month, but will not sort the months into the order they are found in the calendar. It should be considered a 'display' column, and used with column C as the 'sorting' column.
E2 =MONTHNAME(MONTH(B2))&" "&DAY(B2)
Column F displays only the 'age at this year's birthday' for each date in column B. The formula is a subset of the one in column D.
F2: =YEAR(TODAY())-YEAR(B2)&"yrs"
Each of the formulas is independent of the others and depends only on the values in column B (plus the value returned by TODAY() in the formulas calculating an age figure). The formulas for columns C or D may be used to sort the list in accordance with your needs, Those in columns E and F will not sort in calendar order.
Regards,
Barry