It seems logical that if children live with each parent an equal amount of time, neither parent should have to pay child support. In reality, however, it typically doesn't work that way. The parent who earns more must often make a cash contribution to the other parent's household, although it's usually far less than it would have been if joint custody weren't a factor. If parents earn the same, however, this could eliminate the need for child support under some circumstances.
Legal Vs. Physical Custody
One problem with determining whether joint custody will affect your child support obligation is that custody terms can be confusing. In many states, "joint custody" means parents share legal custody, and this has no effect on child support at all. Legal custody only sets guidelines for who makes important decisions on behalf of the children, and this doesn't affect the costs of raising them. Physical custody arrangements do affect child support, however, and many states refer to joint parenting time as "shared custody."
Another complication is that joint parenting doesn't always work out to an exact 50-50 split between parents' homes. Some states take this into consideration by including in their statutes a minimum number of overnights that constitutes shared custody. For example, in North Carolina, the number is 123. In Oklahoma, it's 120. In either case, the custody arrangement breaks down to the children spending roughly two-thirds of their time with one parent and one-third with the other. Although this is considered joint physical custody, the parent who has the children two-thirds of the time has added costs for their care. It wouldn't be fair or logical to eliminate child support entirely under such an arrangement.
Some states, such as New Jersey, break child support down into three components based on what it's supposed to cover. A portion of child support goes to fixed expenses – costs that don't change regardless of where the child is staying that night. Fixed expenses include things like mortgage payments and utilities. Variable expenses cover expenses such as groceries and these tend to increase when the child is in residence. Controlled expenses are those things that a parent has some discretion over spending money on – or at least the parent can decide how much to spend. These include things like clothing costs. The law assumes that controlled expenses tend to fall to the parent who has primary physical custody. In a 50-50 shared parenting arrangement, however, both parents have these costs.
Different states use various methods to calculate child support when both parents have equal costs. Some states employ a complicated formula that includes a deduction for controlled expenses from the "non-custodial" parent's child support obligation because he has the children an equal amount of time so he's taking on some of these costs. In cases where custody is more of a 65/35 arrangement than a 50/50 schedule, child support is typically calculated on the exact number of overnights the children have with each parent. The more overnights a parent has, the lower his support obligation becomes, so even if shared custody doesn't eliminate child support entirely, it invariably reduces it.
Beverly Bird has been writing professionally for over 30 years. She is also a paralegal, specializing in areas of personal finance, bankruptcy and estate law. She writes as the tax expert for The Balance.