How to Calculate Child Support for Joint Custody

Child support calculations are driven by state law.

Although child support constitutes an important issue for all parents trying to raise children in a separated family, individual state laws vary as to how it is calculated and how child support factors–health insurance costs, day care costs and extraordinary expenses, to name a few–are treated in the context of that calculation. Despite these variations in the law from state to state, child support calculations for a joint-custody arrangement will involve a similar set of steps regardless of your jurisdiction.

Step 1

Determine the appropriate child support calculation formula for your state based upon your child-custody arrangement. According to the Nolo website, joint legal custody implies the right to participate in major decision-making events, but joint physical custody relates to the right of placement with the child at certain times. The amount of placement time each party has with a child can influence a child-support calculation in many jurisdictions. In North Carolina, for example, if one party has the child overnight on 123 days per year or less, the percentage of time he has placement does not matter, but it does when he goes over 123 overnights.

Step 2

Calculate your monthly income after reviewing your state's child support laws to determine what constitutes income in your state for child support purposes. If your income is irregular, figure it on a yearly basis and divide it by 12 months to derive an average. If you work in an industry where income varies from year to year, average out the last three years before dividing by 12.

Step 3

Calculate the other parent's income using the same rules you applied to your own. This may become difficult if you suspect the other party is not reporting her income truthfully. In these cases, you may be able to determine her income by comparing what she says she earns against what she spends every month. You may also get a better picture of her income by reviewing her bank deposit records and past credit applications that require her to disclose her income.

Step 4

Calculate the other figures that must be included in a child support calculation in your state. These commonly include health insurance costs for the child, day care costs and extraordinary expenses such as special education, orthodontia and sporting activities.

Step 5

Apply your income figures and expense calculations to the child support formula mandated by your state. You may be able to find a state-specific child support calculator on the Internet to help you.


If you are seeking to receive child support, consider consulting with your local child support enforcement agency. These government services are provided at little or no cost regardless of your income.

Things You'll Need

  • Copy of your state's child support guidelines

  • Your pay information

  • Other parent's pay information

  • Documentation of health insurance costs

  • Documentation of work-related child-care costs

  • Documentation of recurring extraordinary expenses


If you figure a child support calculation incorrectly, it could cost you thousands of dollars. Always consult with an attorney licensed to practice law in your state before taking any action with legal consequences.

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