If every school trip turns into an argument with your ex, agree the rules once, in writing, before the next bill. Worked examples with real numbers, plus messages you can copy for asking, saying no and chasing a late payment.
The money fights that wear separated parents down are often about small things: a $65 field trip, or a text that says “you owe me” with no receipt attached. Agree in writing which costs you share and how you split them, then set up a routine so money moves without a conversation each time. The rules differ between the US, the UK and Canada, and I’ll flag where.
Child support (child maintenance in the UK) is the regular payment from one parent to the other, usually set by a formula. In the US, every state has official guidelines that courts and agencies must generally use, according to the federal Office of Child Support Enforcement. In the UK, parents agree an amount privately or use the Child Maintenance Service (CMS).
The extras sit on top, and some systems already cover part of them. Canada’s Federal Child Support Guidelines have a category of “special or extraordinary expenses” that includes childcare you need for work, uninsured health costs over $100 a year (orthodontics, counseling, glasses), and extraordinary costs for school and activities. As a general rule, parents share those in proportion to income. In the US, federal law requires every child support order to address the child’s health care needs, so yours may already say who pays the orthodontist.
So read what you already have. Where your order or agreement covers a cost, follow it. Where it says nothing, write that part yourselves.
Do this in a quiet week, when nobody is waiting to be paid back. For each item, decide whether it’s shared and who gets to say yes.
The “who says yes” question prevents more fights than the split does. Set an ask-first limit, say $150 or £100. Anything above it needs a written yes before it’s bought, except urgent medical care. Below it, whoever has the child that day buys it and logs it. Without a limit, you keep having one of two arguments: “you signed her up without asking” or “you won’t pay for something she needs.”
Write down what isn’t shared, too. Priya and Sam, parents of Maya, 9, and Theo, 14, made everyday clothes “not shared” after a year of arguing about jeans that never came back from the other house. Theo’s phone is off the list as well: Sam wanted him to have one, so Sam pays for it.
Some costs you can see coming: back-to-school, winter coats, camp deposits due months before summer. Add up your share of last year’s extras, divide by 12, and set that much aside each month.
Half each is the simplest split, and it feels fair when incomes are close. When they aren’t, half of a $1,200 camp is an easy yes for one parent and a month of groceries for the other, and the lower earner starts saying no to things the child would love.
Or split by income. Priya earns $62,000 and Sam $38,000, so Priya pays 62% of shared costs and Sam 38%. On a $4,800 orthodontic bill after insurance, that’s $2,976 and $1,824. The downside is that you have to share income figures, and without a set date to update them, every raise turns into a new argument.
Or each parent owns whole categories: one pays for all sports, the other for school costs and glasses, and nobody reimburses anybody. It suits parents who want as little contact as possible, and it fits parallel parenting. The catch is that categories rarely cost the same. A six-year-old’s Saturday soccer costs little; a fifteen-year-old’s travel team can outspend everything else on the list.
My recommendation: if an income split would come out closer than 55/45, go half each. If it’s further apart, split big items (braces, camps, laptops) by income and smaller ones 50/50, and update the percentages once a year from tax returns.
Whatever you choose, put numbers in it. Justice Canada suggests writing down, for each expense, what it’s for, the total cost, each parent’s share and the due date, and notes that an extra can usually only be enforced when the agreement or order gives a dollar amount for it. “We’ll share sports” means a new negotiation every season. Compare: “Sam pays 38% of Theo’s club soccer: $159.60 of the $420 season, due September 1.”
This routine lets most reimbursements happen without either of you expressing an opinion. Change the numbers to suit you.
For the log, a shared spreadsheet with those six columns is enough. Lullia’s money ledger does the same job with receipts and deadlines attached, and it records payments without ever moving money. For regular child support, the UK government’s arrangement form calls a standing order the best way to get payments in full and on time. For what else is worth recording, see what to write down when you co-parent.
Most of the heat in a money message comes from the history and the “as usual.” Give the other parent only what they need to pay: what it was, which child, the amount, their share, the receipt and a date.
After you’ve paid:
Hi Sam, Maya’s class trip to the science center was $65, paid today. Small items are half each, so your share is $32.50. The receipt is in the log. Could you send it by March 15? Thanks.
Before you spend, when it’s over the limit:
Theo wants to join the club soccer team this fall: $420 for the season, plus about $90 for cleats and a uniform. That’s over our $150 limit, so I’m checking first. Registration closes August 20. Are you OK to pay your 38% ($193.80)? If not, I’ll cover it this season and we can look again in the spring.
When you need to say no:
I can’t do my share of the $1,200 sleepaway camp this year. I can put $200 toward it, or we could split the city day camp ($340) at our usual rate. Could you tell me by Friday which you’d prefer?
The fallback in the soccer message (“I’ll cover it this season”) lets Sam say no without Theo losing his season, so his answer isn’t a test of who loves Theo more. What I’d avoid is promising the child first and presenting the bill as a done deal; even a reasonable co-parent digs in when told instead of asked. For an ex who reads every message as an attack, see how to write to your co-parent without starting a fight.
Check the log first: is the amount right, and has the deadline passed? Then send one reminder.
Hi Sam, the $32.50 for Maya’s trip (logged March 1) is still showing as unpaid. Could you send it by March 22? If money is tight right now, tell me and we can agree on a later date.
Don’t send a second message the next morning, and don’t bring up last year. A single $25 trip isn’t worth escalating.
If it’s the extras that keep going unpaid, change the setup instead of sending more reminders. Ask for the other parent’s share before you book the next big item, or move those costs into whole categories so nobody owes anybody. If the amounts are large, ask a mediator or family lawyer about writing the extras into your order with dollar figures.
A pattern of missed child support is different, and each country has an official route.
In the US, your state or tribal child support agency enforces orders. Some charge an application fee, usually no more than $25, according to the Office of Child Support Enforcement. Whether the agency can help with an unpaid extra depends on what your order says about it.
In the UK, the CMS’s Direct Pay option has no collection fees, but keep a record of payments: if one is missed, you may need to show a bank statement. If the paying parent doesn’t pay in full and on time, the CMS can switch the case to Collect and Pay, which adds a 20% fee for the paying parent and takes 4% off what the receiving parent gets (GOV.UK). In June 2025 the government said it would scrap Direct Pay and charge most parents a 2% fee instead, but that needs a new law first, so check GOV.UK for the rules in force.
In Canada, each province and territory has a Maintenance Enforcement Program that helps enforce support orders and written agreements (Justice Canada). In Ontario it’s the Family Responsibility Office (full list).
If your ex uses money to control you, for instance by threatening to stop paying unless you give in, don’t run a routine that needs direct contact. The UK government’s 2025 response says paying directly between parents is “sometimes used as a vehicle for financial and coercive control.” Use the agency route. In the UK, you can tell the CMS if it isn’t safe for the other parent to know where you live, and GOV.UK suggests a bank account with a “non-geographic” sort code for the same reason.
Incomes change too. In the US, child support doesn’t change automatically, but either parent can ask for a review at least every three years, or sooner after a significant change. In the UK, the CMS reviews the amount every 12 months, and wants to hear sooner if the paying parent’s income changes by 25% or more. In Canada, the route depends on your province, so ask a family lawyer.
Your split for extras needs the same attention. If Sam loses his job, agree on a temporary change in writing with an end date (“Until March 1, Sam pays 20% of extras instead of 38%, and we look again then”). Otherwise payments tend to stop quietly, and nobody notices until April.
What children need to hear depends on their age. Under seven, they need to know they’ll be looked after, not who pays. If a five-year-old overhears an argument about a trip, this is enough: “Mommy and Daddy are sorting out the money. That’s a grown-up job.”
From about seven to twelve, children notice who pays for what, and some start to think they cost too much. Maya, 9, asks, “Is Dad not paying because the trip is too expensive?” She’s really asking whether she’s still going and whether it’s her fault. Answer both: “You’re going on the trip. It’s paid for. Dad and I work out who pays for what, and that’s our job, not yours.” Then stop.
Teenagers understand money, which makes them easy to recruit as messengers. Theo, 14, tells Sam, “Mom says you never pay for anything.” Try: “Your mom and I sort out money between ourselves, and I’m not going to talk about her with you. If you need something, ask me and I’ll take it up with her.” A teenager can also hear that the budget has limits without hearing who owes whom: “Sleepaway camp isn’t happening this year. It costs more than I can spend. Day camp is booked.”
At any age, don’t send money or checks with your child, don’t ask them to ask the other parent for money, don’t tell them the other parent is behind on support, and don’t let them see the log.
Before the next bill arrives, write down:
Send it to the other parent as a proposal and expect them to change a number or two. If you can’t agree, take this page to a family mediator. If direct contact isn’t safe, skip the proposal and use your child support agency.
This is general information, not financial or legal advice. Check with a family lawyer or mediator where you live.