The table below gives the minimum and maximum number of weeks needed to cover a given number of months.
number of months 
minimum number of weeks 
maximum number of weeks 

number of months 
minimum number of weeks 
maximum number of weeks 
1 
4 
6 

7 
31 
32 
2 
9 
10 

8 
35 
36 
3 
13 
14 

9 
39 
41 
4 
18 
19 

10 
44 
45 
5 
22 
23 

11 
48 
49 
6 
26 
28 

12 
53 
54 
This table is generic in the sense that it does not assume, for example, that a 6 month period runs from January to June and July to December. It looks at the minimum and maximum number of days that can be contained by any given number of contiguous months.
This table is often used to determine the number of possible weeks that a backtrack every page grid would need, or in the rarer case of extended minicalendars.