He is lying to you.
- Most people open bank acounts online . I have more than 10 accounts and I haven’t gone into a branch to open one since the 1980s.
- once the account is open, the bank staff have no idea how the money in the account is managed, who puts in how much etc
- The money in a joint account isn’t owned 50:50 - you both own all of it.
So he is lying to you to get his own way / win an argument. I suggest you file away that piece of information for future reference .
IMHO the fairest way to split shared costs is in proportion to your income . Especially if one person in the couple has taken time out of work or unpaid leave or part time to care for children/elderly relatives in order to facilitate the other person’s career.
As you mentioned “going back full-time“ my guess is that this is you so you have been the one who has sacrificed your own career promotion opportunities and pension/savings to allow your husband to work full-time while you take on more of the unpaid work.
So it would be doubly unfair if you were penalised twice for this thing that you have done to help his career.
The other thing I suggest you do is make sure that all housework childcare and wife work are divided equally between you now you’re going back to work. I’m sure he will approve of this as he’s very keen to be fair and equal.
There are lists online that you can use to make sure that all tasks are covered. It’s easy to forget this that are irregular but take a lots of time , like making medical appointments for children, arranging time off work / school and taking them there. Or dealing with birthday party invitations , buying gifts and taking kids to and from parties / events .
If you do decide to keep your money separate, you will need to have a very detailed record / breakdown of all individual spending that is for something that should be joint. For example, if you collect the children from a club and take them to McDonald’s, that needs to come from the joint spending. If there is no joint account, you’ll have to take a note of this money and then get him to settle up with you at the end of the week/month.
If you have a car then you will need to get a tracker / app which logs every journey so you can go through it weekly and classify every journey as personal or joint . Some trips have a shared purpose eg you go grocery shopping on the way home from work , then pick up a child from football and go home. How do you divide that up ?
As you can see this becomes very complicated and creates a lot of work which is why most couples have a joint account. That way the spending for the children’s club/McDonald’s/new school shoes/ class trip can all come from one account .
I also find that lots of fathers have no idea about all these additional costs as they have not spent much of their lives dealing with the complexity that is bringing up children. So what happens is that mothers just end up absorbing all these costs into their share while their husbands sit and shake their heads and say “I don’t know how you end up spending so much money“.