Most arguments about money between two homes are not about the amount. They are about being asked to trust a number with nothing behind it.
School fees, uniforms, the gap on medical bills, sport, music, the phone. Write the list down once, while nobody is annoyed. Almost every argument later is about whether something belonged on the list, not about the percentage.
A haircut, a birthday present, an outing on your own week. That rule sounds harsh until you notice how much it takes out of the conversation, and it protects the parent with less money from being billed for the other parent’s ideas.
Half each is simplest. Splitting in proportion to income is fairer and harder to keep current. One parent covering a whole category — you take sport, I take uniforms — avoids arithmetic altogether. Any of the three works. Changing it halfway through a year is what causes trouble.
Photograph it at the till. A figure typed from memory three weeks later invites a question, and the question is what starts the argument. It matters more again if you ever have to show a third party what the year actually cost.
Once a month, same date, whatever the balance is. A running total that never closes turns every purchase into a negotiation and every negotiation into a mood. Closing the month is what keeps money boring.
Braces, a school trip, a laptop, a season of something expensive. Ask first, in writing, with the price in the message. A parent who was asked will usually pay. A parent handed a bill will usually argue, even when they would have said yes.
Child support is set by a formula or an order, and it is not the same thing as splitting an excursion fee. Keeping the two apart, in your head and in your records, stops either one being used as an argument against the other.
Write the shared list. Agree one split. Pick a settle-up date. Then photograph every receipt for a month and watch how much of the usual friction simply stops appearing.
This guide is general information, not legal or financial advice. Child support rules, and what counts as a shared expense, differ by country and by case.