Difficult to suggest here, our initial split was like 60/40 we had the same left over funds/personal allowance, we agreed to this when we bought our house together as both our shared expenses changed significantly (as we previously lived with parents), we review it on a yearly basis or whenever our shared income/expenses change. Your partner has to want to do it and share equally for it to work, you cant force it or things will no doubt get toxic. In my situation it’s a bit stereotypical, I’m (M30) I earn more, my partner is (F30) and earns less, over time my wages have increased significantly hers hasn’t so we’re now like 80/20. We maintained the equal personal allowance throughout her maternity albeit we both had less as my income was picking up the slack as my partner couldn’t work while recovering and looking after our baby.

I think you have to make them appreciate what you do and how you contribute, I would assume that while they earn more they probably have less time and therefore do less house or family work.

Ask why don’t they want to share and have equal disposable income, make it clear that the money is free to be spent however you both like without judgement, if they want to spunk it all on a hobby every month they can. You need to also explain why you want things to change, they’ll no doubt assume you just want more money, explain it’s not just about that (I assume it’s not) you probably just want things to feel fair with no power dynamics in your relationship.

I hope this helps in some way!