Ok, this is not as straightforward as it might seem. (Or maybe it is and I have got it wrong). I have NC for this as don't want it following me around but have been here since Pom Bears and NAICE ham and am a regular on The Archers threads. Anyway, here is my thinking.
I live with DH, Dd14, DS18 and (at the moment) DD20.
Ds18 is about a 7/10 on the idleness scale. He is very hard to get to do anything housework wise. Eg. Wash up. He will do this quite badly, leave food in the sink and no surfaces wiped.
Hoovering - he'll do upstairs but not down unless I nag. He took a year out before going to Uni but has just squandered the time in bed until I made him get a job.
He now works at the local large pub/restaurant about 5 days a week 12-4pm then 6-10/11pm. He takes home about £280 a week. Out of which I charge him what I think is a very generous £30 per week. This covers food and utilities. (His girlfriend also stays over two weekends a month)
Now, DD20 is back from Uni. She is a completely different kettle of fish. I don't have to ask her to wash up, she just does it. The kitchen looks like a professional cleaning company have been in. Same with hoovering/bathroom cleaning.
DH and I both work full time. Have done since DD20 was three months. I can't tell you how lovely it is to come home to a clean and tidy house after a long commute ! This ONLY happens when DD20 is home from Uni. When it's just Dd14 (quite helpful but not great) and fairly revolting Ds18, arriving through the door is quite depressing.
So....DD20 is working at same pub as her brother for the summer. Earning pretty much the same money. I told her that I would have to charge her £30pw as I charge her brother that. She insists that she shouldn't have to pay as A. She hasn't wasted her time lying in bed, worked really hard got into a great Uni and this is her holiday.. She needs ALL her money to pay for next year. and B. Her 'rent' is covered in her ability to be competent at housework...and she is saving me and DH from redoing the things DS18 should have done.
DS has not passed comment. - They get on very well, so there will be no falling out with each other over this, either way.
Should I charge or not.