I have had my current build for 3 years. I try to get as much out of my computer before I upgrade. I have been waiting for prices to go down so I can get a VR ready setup going. So once that happens I will be upgrading and building a new PC.
Regarding my phone, I'm not really in any big hurry to upgrade (I'm not that type that has to have the newest thing available right when it comes out, though my boyfriend is ), but it depends on what's out and if I have the option to upgrade without having to pay a ton of money to do it. But I tend to upgrade my phone about every 2 years or so.
For a while I got a new phone each year, I went iPhone 5 > 5s > 6 but before that I went 4 > 5 and I am I waiting for the next iPhone to upgrade from my 6. So 1-2 years for phone. 2-3 for tablet, 5-7 for computer.