Was trying to explain to someone who thought I was crazy for getting the iPhone 6S Plus when I just got the iPhone 6 Plus last year and am not eligible for an upgrade. Got me thinking about my true cost of an upgrade. I got my 6 Plus for $499 on a 2 year contract last year. This doesn't change whether I upgrade this year or next. I sold my 6 Plus 128GB for $620. I am buying the 128GB 6S Plus for $949, with a 10% discount from paying with Apple Pay. This comes to $908 purchase including tax minus the $620 so $288. However, what also must be considered is opportunity cost. In a year, how much more can I sell the 6S Plus over the 6 Plus? I don't have a good feel for this but guesstimate it must be at least $150-$250. This makes the upgrade from $0 - $100 total cost. Been trying to explain this to my fiancee and a friend but they don't "get it". Seems like if you privately sell your phone, a yearly upgrade is almost a no brainer. Any thoughts on this or similar experiences/viewpoints?