Anonymous
Don't know. I wait till it breaks.
fuzzy
Depends on the bike, how it's ridden, the chain quality & maintained.
I used to get 1 to 5 thousand miles on a Honda CB350. The low figure was a cheap Chinese bit of junk. This was pre O ring chains. Normal procedure was to oil it weekly + after riding in the rain.
Anonymous
Use, maintenance and type of bike will make a difference.
12k miles is not impossible.
thebax2006
Chains stretch as they are used. The way to decide if the chain need replacing is to look a the sprockets they drive. If the drive gear sprocket is egged shaped replace the motor sprocket, the wheel sprocket and the chain.
CB
20-30k for o-ring type chains if kept cleaned and lubed properly.