DS is 17 and in Y13. Since starting 6th form I give him £80 per month. This is supposed to cover socialising and anything he wants, including meal deals etc if he doesn't want to make a packed lunch. This was in line with what ds1 got, but he got a part-time job to top it up. Ds2 hasn't found one, though he hasn't tried that hard either. However, he doesn't go out much and therefore it's been enough and he hasn't complained. I also pay for his phone - £15/20 per month.
I have never believed in making them earn an allowance and have instead gone down the road of 'we all live here and need to do certain things to keep the house ticking over/be a functioning human and, yes, as your parent it is my responsibility to give you an (affordable to me) amount for recreation'. He does his own laundry (with reminders) and is obviously supposed to put his plates in dishwasher/unload it if he's home when it's done and other very minor things I ask as and when - these are minimal. Also, I have an en suite so he (they when ds1 is home from uni) is supposed to keep the main bathroom clean. None of this has ever been linked to the allowance.
However, I am getting really sick of how messy ds2 is and how little he does without being prompted. His bedroom got absolutely ridiculous last year and he spent 5 days over the summer (slowly) sorting it, and is making no effort whatsoever to keep it tidy. He has to be asked and reminded to do things every single time. Plates are either left wherever or taken to the dishwasher but not put in. Bathroom is left until I explode. I mean, he's not dirty really - it's all mess rather than filth, but I'm sick of having to ask/nag/shout for stuff to be done.
I'd like to tell set out some minimal things I'd like done automatically without me asking, and if not cut the allowance, but I'm not sure how to go about this as I feel it's moving the goal-posts. The other thing is, I'm conscious of fairness as I never did this with ds1. However, his room, though not tidy, was never as bad, simply because he was never in it other than sleeping. He was also a lot more active and busy, but I don't really think that's fair of me to penalise ds2 for being more of a homebody. Finally, ds2 is learning to drive and ds1 didn't want to. That means ds2 is currently costing me £200 per month in 'extras' and I do feel it's a bit ridiculous he can't even take a plate to the dishwasher without being told.
He's a lovely kid though - no trouble, working hard at A levels and doing well and, despite needing a bit of nagging, he is generally compliant and pleasant. I don't want to wreck our relationship when it's his last year at home!