Very Simple Android App

i need a very simple android app to calculate weeks and days starting from one given previous date example of what needed : ====================== starting date --> set to 2 July 2012 right now (today 31 july 2012) --> (the app makes calculation and gives result) 4 weeks and 2 days ===================== second feature: starting date --> set to 2 july 2012 , counter set was 2 weeks and 0 days right now (today 31 july 2012) --> (the app makes calculation and gives result) 6 weeks and 2 days =================================== the aim of the app is to calculate pregnancy term , first by last period day , and second feature by first ultrasound exam means i have to choose option 1 or 2 when loading the app , then i set variables to make the calculation