Co-Parenting Expense Rules in California (2026)

How California Handles Shared Child Expenses

California uses a two-tier system for child expenses after separation or divorce. The first tier is guideline child support — a monthly payment calculated using a statewide formula. The second tier is add-on expenses — specific costs that parents share on top of basic support.

Understanding which expenses fall into which tier is critical. If an expense is already covered by guideline support, you generally cannot ask your co-parent to pay extra for it. But if it qualifies as an add-on under Family Code 4062, your co-parent has a legal obligation to share the cost.

What Basic Child Support Covers

California's guideline child support formula (Family Code 4055) considers each parent's income, tax filing status, and the percentage of time each parent has physical custody. The resulting monthly payment covers the child's ordinary living expenses: housing, food, clothing, basic transportation, and routine school supplies.

This means if you buy groceries, school uniforms, or everyday clothing for your child during your parenting time, those costs are considered covered by guideline support. You typically cannot seek reimbursement from your co-parent for these routine expenses.

The guideline calculation is done using software called DissoMaster (or XSpouse), which California courts rely on heavily. You can estimate your guideline amount through the California Courts self-help website.

Add-On Expenses Under Family Code 4062

This is where most co-parenting expense disputes happen. Family Code 4062 defines two categories of add-on expenses:

Mandatory Add-Ons (Section 4062(a))

Courts must order parents to share these costs:

• Childcare costs related to employment or reasonably necessary education/training for employment
• Uninsured health care costs for the child — this includes co-pays, deductibles, dental work, orthodontics, therapy, vision care, and prescription medications not covered by insurance

These are not optional. If one parent incurs a qualifying childcare or medical expense, the other parent is legally required to contribute their share.

Discretionary Add-Ons (Section 4062(b))

Courts may order parents to share these costs:

• Extracurricular activities — sports teams, music lessons, dance classes, summer camps
• Educational expenses — tutoring, private school tuition, special education costs
• Travel expenses for visitation
• Special needs costs — therapy, specialized equipment, adaptive programs

For discretionary add-ons, courts consider whether the expense is reasonable given the family's overall financial circumstances and whether it is in the child's best interest.

The 2024 Change: Proportional Income Splits

This is the most significant recent change. In September 2024, Assembly Bill 1755 (AB 1755) amended Family Code 4061 to change how add-on expenses are divided between parents.

Before AB 1755: Add-on expenses were split based on each parent's "respective net disposable incomes" — but in practice, many courts defaulted to a 50/50 split unless one parent requested otherwise.

After AB 1755 (effective September 1, 2024): Add-on expenses are now explicitly split in proportion to each parent's net disposable income, unless the court orders a different allocation for good cause. The 50/50 default is gone.

This matters. If one parent earns significantly more than the other, the higher-earning parent now bears a proportionally larger share of add-on expenses.

How to Calculate Your Split

Here is a practical example:

• Parent A earns $80,000/year net disposable income
• Parent B earns $40,000/year net disposable income
• Combined income: $120,000

Parent A's share: $80,000 / $120,000 = 66.7% Parent B's share: $40,000 / $120,000 = 33.3%

Now apply this to actual expenses:

This is on top of whatever guideline child support Parent A already pays.

Do Both Parents Need to Agree on Expenses?

This is where California law gets nuanced:

Mandatory add-ons (childcare, medical): These do not require the other parent's consent. If your child needs medical treatment, you should get it. Courts will order reimbursement regardless of whether the other parent agreed in advance. However, for non-emergency medical decisions, it is good practice to notify your co-parent.

Discretionary add-ons (extracurriculars, education): These generally require either mutual agreement or a court order. One parent unilaterally enrolling a child in a $5,000 summer camp does not automatically create a shared expense obligation. If your co-parent did not agree to the expense and there is no court order covering it, you may be stuck paying the full amount.

Best practice: Get written agreement from your co-parent before incurring discretionary expenses. A simple text or email saying "I'd like to sign the kids up for swim team — $200/month, our shares would be $134/$66 based on income. Do you agree?" creates a record that protects both parents.

Documentation and Tracking Requirements

California courts expect parents to keep clear records of shared expenses. When disputes arise, the parent with better documentation almost always has the advantage. Courts want to see:

• Receipts and invoices for every shared expense
• Proof of payment (bank statements, credit card records)
• Communication records showing the expense was discussed or agreed upon
• A clear accounting of who paid what and what reimbursement is owed

This is exactly the kind of tracking that becomes difficult with spreadsheets or text messages, especially as expenses accumulate over months and years.

What to Do When Your Co-Parent Won't Pay

If your co-parent refuses to pay their share of a legitimate add-on expense, California law provides several options:

1. Informal communication — Start with a clear, written request. Include the receipt, the amount owed, and the statute reference (Family Code 4062). Sometimes co-parents do not realize they have a legal obligation.

2. Mediation — Most California counties require mediation before you can get a court hearing on family law disputes. This is usually free through the county's Family Court Services. Mediation is often faster and less adversarial than going to court.

3. File a motion with the Family Court — If informal negotiation and mediation fail, you can file a Request for Order (FL-300) asking the court to order reimbursement. Under Family Code 290, the court may also award attorney fees to the prevailing party in enforcement actions.

4. Contempt proceedings — If there is already a court order specifying expense sharing and your co-parent violates it, you can file for contempt. This is a more serious legal action and typically requires an attorney.

Key Statutes and Resources

• Family Code 4055 — Guideline child support formula
• Family Code 4062 — Add-on child care and health care costs
• AB 1755 (2024) — Amendment making add-on splits proportional to income
• California Courts Self-Help: Child Support — Free resources and forms
• DissoMaster / XSpouse — Software used by California courts for guideline calculations