My ex-partner ‘demanded’ that I pay 50% of our daughter’s medical expenses. He earns 3 times my salary. Is that fair?

So here’s my question: When there’s a big disparity in pay — is 50% of dinner, mortgage, medical bills, vacation, utilities and other shared expenses justified? 

Wouldn’t a more equitable solution be based on income? Like if I make $50,000 and my partner makes $150,000, wouldn’t an equitable arrangement be for me to pay 25%? 

I know now that money should be a frank and practical discussion in any situation, but I’m wondering what your take is on this. 

Mother Left Holding the Bill

Dear Rebecca,

There’s rarely such a thing as “fair” in a breakup, especially when it comes to finances. 

If one ex is paying alimony and child support, they may leave the marriage with years of lingering resentments over how much they have to pay their ex. For a couple that had a child together, and did not get married, the issue is more complicated but the absent parent is compelled by the law to pay child support. In that case, child support pertains to the responsibility for raising a child. 

For parents who never married, it’s harder to argue that you should only pay medical bills for your child in proportion to your incomes. Usually, you would leverage your child support to pay for such expenses and/or — when appropriate — ask your former partner to pay their share. If you were married and divorced, the divorce decree should specify how much money each former spouse should pay for their child’s education, living expenses and medical bills. 

Katie Carter, a divorce attorney with the Hofheimer Family Law Firm in Virginia, has opinions on this issue: “In lots of agreements, I find that opposing counsel (especially when the husband earns more) will try to include that the parties will split the unreimbursed medical expenses 50/50,” she writes. “But that’s not the law. The law says that the parties will split unreimbursed medical expenses pro rata – that is, proportionally, based on their incomes.”

Bottom line: “If he earns 80% of the income, he pays 80% of the unreimbursed medical expenses, she adds. “I would only ever agree to a 50/50 split if the parties’ incomes were equal, or if a pro-rata split would mean that my client would pay more of the expenses. Again, it’s important to look at these numbers. Even if the distinction is only 60/40, it can make a big difference if there’s (heaven forbid!) a catastrophic accident or a bad diagnosis of some kind.”

I’d hate to think of any marriage where a higher earning spouse nickel-and-dimed their partner, forcing them to cough up 50% of a vacation or dinner, but these are all good conversations to have ahead of time. If both partners are working and you can afford a larger home because the husband or wife earns three times their spouse’s salary, it would seem churlish to expect both partners to split the mortgage or dinner out 50/50. But some people love to count!

You can email The Moneyist with any financial and ethical questions at qfottrell@marketwatch.com, and follow Quentin Fottrell on Twitter.

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