How to make contribution to the household fair

[Petsgalore]

So far we have not asked for any contributions towards the household DS22 is at Uni and has a part time job, DS19 gets a good income from a full time job, I think it would be good for them to both understand the cost of things, how have others done this would you ask for a percentage to contribute towards food etc

Depends on the child and state of maturity
is the contribution needed because you need more money, you would like more , or would it be saved for when they finally move ?

I would estimate how much is would cost them to live on a house share - rent and share of bills and get them to do the same

then if I needed to cover bills I would show them the current problem and split the gap between them - so 50 a week from each if you are short of 400 a month

if they are saving to move out , then 75% of what it would cost them to live out

the third case is the hardest - it seems like making a point

I would charge - their food and obvious bills ( so would you ge council tax rebate if they left ?) do they cost a lot on electric for games or baths ? Anything clearly just their cost

My 20yo is doing a professional apprenticeship.
He pays £100 per month, and buys & cooks his own food.