Some programming

Once in a while I just like to do some programming.
Usually it is something rather simple (KISS), but it keeps my mind busy (and healthy, I hope).
My current program is a little app for my mobile to keep track of the date when to get a new load of pills. Until now either I calculate the dates over and over again, or I have it on paper (and then lose it).
My program  should be doing the calculation for me.
Of course I know, when I look at my pills, that the time to go to my GP and then the pharmacy is close. But not how close.

The tool I am using is MIT App Inventor. Quote: MIT App Inventor is an intuitive, visual programming environment that allows everyone – even children – to build fully functional apps for Android phones, iPhones, and Android/iOS tablets. It is free, and definitely doesn't have a lot of functions. But it is easy.
As so often with programming, the logic is the difficult (and interesting) part. How to achieve a goal? And second difficulty is the weird reaction of your programmed code. I come from Mainframe, pretty straight forward. Already coding on a pc was a new world. Mobile phones are even worse.