Help with remembering Nuvaring

I just started on nuvaring and want to be able to remind myself when to insert and remove it. However, I cannot figure out how to put it in my google calendar so that it correctly spaces out 21days in and 7 days out. It gets a few days off the farther out the calender goes. The nuva ring website doesn't seem to work correctly, at least not from my phone. I downloaded an app but I'm not sure that I trust it. What does everyone here use to keep track?