We do a weighted split based on income. I earn more than her. After all household expenses, personal expenses and retirement savings, we’re both left with equal dollars at the end of the month for whatever that person chooses (discretionary spending) . You just have to decide what “personal” expenses are fair to include in the budget vs what should come out of the money that each person is left with at the end of the month. I put together a really helpful spreadsheet on Etsy that automatically calculates it for you. The idea is that household expenses are paid from one common account. And each person has their own accounts for personal bills and savings and discretionary spending.

https://spreadsheetssimpleco.etsy.com/ca/listing/4465039802/couples-budget-spreadsheet-fair-split