How to count weekly plan & weekly plan's achievement date

how to count weekly plan date as well as achievement date in a month
ie :- colum A colum B

1 2-4-12 4-4-12
2 3-4-12 8-4-12
3 4-4-12 5-4-12
4 5-4-12 7-4-12
5 6-4-12 8-4-12
6 7-4-12 9-4-12
... -------- -------
... ------ ---


30 30-4-12 2-5-12


1. i want to count 1st week column A dates.
2. that 1st week plan how many column B achievement dates.

that answer will come in column C(1st week plan) and D (1week active)