What kind of rent/housekeeping is reasonable to ask an adult (21) child to pay?

[AJ65]

My step son's mother is about to kick him out and we'll probably have him here. He's working, so should we ask a proportion of his salary, or a fixed amount?

While I'm here - shouldn't there be a specific topic for issues with adult children, especially as so many parents find thier children coming home to roost again in their early twenties?

20 percent for room and untilities. Evening meal provided, but if he wants anything outside.of the usual food shop then he gets it himself.

Does own laundry, buys own toiletries etc.

30% sounds very fair to me.

Thanks for all the responses. We've decided to charge him 30% of his earnings if he comes to live with us.

btw - his Mum is only thinking about kicking him out because he's not getting on with his sister and she's studying an access course this year to get into Uni next year and needs peace. He lived with us before and the only arguments were over teenage issues like playing video games when he was supposed to have gone to bed, so there shouldn't be any problems now and his little sister, my daughter, will be ecstatic to have him home!

LOL - didn't realise this had gone onto two pages and was puzzled as to why my responses weren't posting....

I pay £250 a month to live in a flat with my DP (so £500 in total) I think charging him £550 a month is extortionate!