My experience on a 9 speed bike is that you can safely get 8000km/5000mi out of a chain in a flat dry place like Texas. For me that was about once a year, and l

My experience on a 9 speed bike is that you can safely get 8000km/5000mi out of a chain in a flat dry place like Texas. For me that was about once a year, and lubricating it 3x a year. Once you add in bike racks/panniers, trailers, hills, rain, snow, sea spray, sand/grit, etc you may need to reduce service intervals. There are different schools of thought about cassette wear etc. If you have a 10 or 11 speed bike, which have very thin/lightweight chains (9 speed chain is considerably larger/beefier) then you probably need to shorten your service intervals even shorter. 11 speed chains in particular seem to be very expensive and have relatively short lifespans. That said, changing a chain on a bike takes about 2 minutes with the quick release links they come with now. It's probably more effort to take the bike to the shop than it is to do it yourself.