Help with condition format or formula to identify a leap year date in a cell

I have attached a sample sheet.
I am doing a number of worksheets that will all take the start date from sheet 1. each sheet covers a 3 month period.

starting at 31/1/12 the next date is 30/4/12 so it just adds 90 days and then similar for the next 3 month periods.
The problem is that 2012 is a leap year so there are more days in February, so in 2013 the same calculation takes the next period to 1/5/2013 and then has a knock on effect for the following periods.
The work book will cover a few years so I could do with a conditional format or a formula if possible to identify a leap year from the initial start date. It will probably be easier to refer to my sample sheet to get a better idea of what I'm after.
Thanks