Splitting the cost of parenting with an ex can be a difficult conversation to bring up. How can you suddenly shove half of a medical bill onto your ex? Should you have to cover sudden extra school trip expenses, even if you didn't want to send your child on the field trip?
First of all, it's very important for you and your ex to communicate. If your ex wants to spend too much money on something extra for your child and wants you to foot some of the bill, talk about why you don't want to. You may find that your reasons for not paying part of the bill was simply down to not understanding why your child needed to participate, or you could find that your ex agrees that the extra expense isn't necessary.
You can also create a system for situations that arise. Consider this: If a court believes the extra expense is necessary or reasonable, it's likely you'll have to split it. So, consider your situation and what's fair. Are you eager for your child to play a sport that your ex doesn't care much about? Suggest paying for most of it, but asking for extra for a uniform or photos of the team. Does your ex want to enroll your child in extra-curricular courses you find important? Then you can split the bill.
You can decide on when you won't pay for an activity, too. Does that extra zoo trip seem ridiculous? Let your ex pay in full. If you want to go to the science museum with your child, you pay for it in full. You can still have solo experiences with your child without having to split the bill, and that may help alleviate some of the tension over who has to split cash for days out.
Source: U.S. News and World Report, "How to Split Parenting Expenses With Your Ex," Geoff Williams, July 23, 2015