Get a park tools chain guage,
like this
Check the chain every few weeks, keep the chain regularly clean and well lubed they will last a very long time.
The 9 sp chain on my dawes galaxy has done 5000 miles and is still well under 0.5% stretched, the chain on my Bianchi 10sp has done 2000 mainly dry miles but very hard miles and is also still under 0.5%. Both these bikes have the chains cleaned and relubed on a semi religeous basis.
The chain on my MTB lasts less than 1000 miles due to the amount of grit and dirt it collects off road
Russell