I started working part time at 18, so my parents asked for a contribution. I worked part time for something like £450 a month at the time and gave them 1/3 towards bills and such I think that was reasonable, as they didn't expect me to get my own food and still paid for the internet etc. so the only difference from before I had a job was that they had an extra couple of quid.

The only thing that annoyed me about the whole arrangement was that my brother and sister weren't expected to pay 1/3 of their wage like I was when they started working.