What happens if there’s essential DC spend but one parent can’t afford it?
It would be a shared cost - well it would for everyone I know who has separate finances.
I’m not (and I don’t think others are, either) talking about separate finances to the extent that you would be splitting individual bills or ‘you pay this bit, I’ll pay that bit’ type arrangement.
DP and I both pay into a joint account each month which covers everything like bills related to our main home, holiday home, all household bills, groceries, holidays, home improvements, school fees (uni fees now) anything DD needs, etc, etc. There is also a big surplus in the joint account and periodically that gets put into a joint savings account, if there’s an interest rate benefit to be had.
It’s just that we have our own separate finances, too, and pay for our own cars, clothes, extra holidays and nights out with friends, etc, etc.
We need £x,xxx per month going into the joint account and we pay it roughly proportionally based on our net annual incomes, although incomes varies with bonuses, etc.
The main thing is that we each have money which is absolutely our own. Not a share of a joint account. Not money we agree with each other to spend. It’s our own. If I wanted to spend £5k on a designer bag (I wouldn’t) it would be no concern of DP’s.