Lumia925 :
Do you have a planned upgrade schedule?
Do you keep using your current laptop till it breaks or stops supporting some attachment/ software?
How often do you get a new laptop?
Depends what you need it for, how well the hardware holds up over time, etc. For example I've got a windows XP laptop I built back in 2005 that runs perfectly today (except the battery life isn't great after being used for 10 years, I could purchase a new battery if I needed to). It depends largely on how well you treat it...