Generating date ranges

Perhaps this way:

Table[DatePlus[{2012, 4, 24}, 28*i], {i, 1, 40}]

{{2012, 5, 22}, {2012, 6, 19}, {2012, 7, 17}, {2012, 8, 14}, {2012, 9, 11}, {2012, 10, 9}, {2012, 11, 6}, {2012, 12, 4}, {2013, 1, 1}, {2013, 1, 29}, {2013, 2, 26}, {2013, 3, 26}, {2013, 4, 23}, {2013, 5, 21}, {2013, 6, 18}, {2013, 7, 16}, {2013, 8, 13}, {2013, 9, 10}, {2013, 10, 8}, {2013, 11, 5}, {2013, 12, 3}, {2013, 12, 31}, {2014, 1, 28}, {2014, 2, 25}, {2014, 3, 25}, {2014, 4, 22}, {2014, 5, 20}, {2014, 6, 17}, {2014, 7, 15}, {2014, 8, 12}, {2014, 9, 9}, {2014, 10, 7}, {2014, 11, 4}, {2014, 12, 2}, {2014, 12, 30}, {2015, 1, 27}, {2015, 2, 24}, {2015, 3, 24}, {2015, 4, 21}, {2015, 5, 19}}

Of course you might want to finetune the number of 28-day intervals.

You can use the built in Calendar functions :

Needs["Calendar`"]

Floor[DaysBetween[{2012, 4, 24}, {2015, 12, 31}]/28]

(* 48 *)

NestList[DaysPlus[#, 28] &, {2012, 4, 24}, 48]

Single liner using currently available commands and avoiding the legacy issues.

NestList[DatePlus[#, 28] &, #1, 
   Round[DateDifference[##2]/28]] & @@ {{2012, 4, 24}, {2015, 12, 31}}