Or (I dont like this now Ive seen Macropod's much shorter formula!)
=QUOTIENT(A1-DATEVALUE("01/"&TEXT(A1,"mm/yyyy")),7)+1&LOOKUP(QUOTIENT(A1-DATEVALUE("01/"&TEXT(A1,"mm/yyyy")),7)+1,{1,2,3,4,5},{"st","nd","rd","th","th"})&TEXT(A1," dddd")
01/01/18 | 1st Monday |
02/01/18 | 1st Tuesday |
03/01/18 | 1st Wednesday |
04/01/18 | 1st Thursday |
05/01/18 | 1st Friday |
06/01/18 | 1st Saturday |
07/01/18 | 1st Sunday |
08/01/18 | 2nd Monday |
09/01/18 | 2nd Tuesday |
10/01/18 | 2nd Wednesday |
11/01/18 | 2nd Thursday |
12/01/18 | 2nd Friday |
13/01/18 | 2nd Saturday |
14/01/18 | 2nd Sunday |
15/01/18 | 3rd Monday |
16/01/18 | 3rd Tuesday |
17/01/18 | 3rd Wednesday |
18/01/18 | 3rd Thursday |
19/01/18 | 3rd Friday |
20/01/18 | 3rd Saturday |
21/01/18 | 3rd Sunday |
22/01/18 | 4th Monday |
23/01/18 | 4th Tuesday |
24/01/18 | 4th Wednesday |
25/01/18 | 4th Thursday |
26/01/18 | 4th Friday |
27/01/18 | 4th Saturday |
28/01/18 | 4th Sunday |
29/01/18 | 5th Monday |
30/01/18 | 5th Tuesday |
31/01/18 | 5th Wednesday |