12 weeks 5 days
45 weeks and 1 day.
In January 2012 there were 4 weeks and 3 days.
5
Including January and March, it's 13 weeks. In regular years it is 12 weeks and 6 days, and in leap years it is exactly 13 weeks. If referring to the period from the beginning of January to the beginning of March or from the end of January to the end of March (or middle to middle, etc.), it is eight weeks and three days in regular years and eight weeks and four days in leap years.
13 weeks
39 weeks and 3 days
21 weeks and 5 days!
The period is seventeen weeks and four days inclusive.
A little over 12 weeks from 1st January 2011 until 31st March 2011.
A little over 43 weeks between March 4 2010 and January 5 2011.
4
11 weeks and 5 days.