What is a pro-rata expense split in co-parenting?

A pro-rata split divides each shared child expense in proportion to each parent's share of combined income, rather than 50/50. If one parent earns 65% of the combined income, they pay 65% of each cost.

Which expenses are usually shared between co-parents?

Typically uninsured medical and dental costs, childcare, school fees and supplies, extracurricular activities, and agreed-upon extras like tutoring or braces. Day-to-day costs in each home are usually not shared.

Shared Expense Split Calculator

List the shared child expenses, mark who paid, and see who owes whom — both under a straight 50/50 split and under an income-proportional split.

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Parent A nameA monthly incomeParent B nameB monthly income

Expense	Amount	Paid by

50/50 split

Parent A owes Parent B $82.50

Each parent responsible for $487.50.

Pro-rata split (59% / 41%)

Parent A owes Parent B $168.53

Parent A responsible for $573.53, Parent B for $401.47.

Total shared expenses: $975.00
Paid by Parent A: $405.00
Paid by Parent B: $570.00

50/50 or pro-rata?

A 50/50 split is simplest and is what most informal agreements default to. Courts more often order a pro-rata split — each parent pays the same share of costs as their share of combined income — because it keeps a large income gap from pricing one household out of activities and medical care.

Whichever you use, put the percentage, the receipt deadline, and the reimbursement deadline in writing. Download the shared expense reimbursement log to keep the paper trail, or let CustodyTrac's expense tracker calculate and log it automatically.

Last reviewed August 19, 2026·Reviewed by the CustodyTrac editorial team

How this is calculated

Pro-rata figures use each parent's share of combined income — the same proportional method income-shares states apply to add-on expenses such as childcare and unreimbursed medical costs.

CustodyTrac publishes educational information, not legal advice. Custody and support outcomes depend on facts a calculator cannot see — confirm anything that matters with a family law attorney in your state.

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Where this fits in a real custody case

A calculator answers one question. These pages cover the record you'll need behind it.

Free co-parenting app for both parents
Shared calendar, messaging, expenses, and court-ready exports at no cost to either household.
Shared custody calendar
Color-coded parenting time both households see, with swap requests built in.
Shared expense tracking with receipts
Split costs, attach receipts, and keep a running reimbursement balance.
Court-ready PDF legal exports
One-click evidence packets for your attorney or a hearing — unlimited and free.
Free OurFamilyWizard alternative
Same calendar, messaging, and export workflow without the per-parent subscription.
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Shared Expense Split Calculator

50/50 or pro-rata?

How this is calculated

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Where this fits in a real custody case

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