How Child Support Is Calculated in New Hampshire

New Hampshire child support is not a number a judge picks out of the air. It comes from a formula in state law, RSA 458-C, based mainly on both parents' incomes and the number of children. Here is how that formula generally works and what can change the result.

The basic idea: combined income, shared responsibility

New Hampshire uses what is often called an "income shares" approach. The court adds both parents' incomes together, applies a percentage based on the number of children, and then divides that total support amount between the parents in proportion to what each one earns.

The parent who earns more pays a larger share. In most cases, the parent with less parenting time pays their share to the other parent as child support.

Step 1: Figure out each parent's income

The calculation starts with each parent's gross income, which is broadly defined. It can include wages, self-employment income, bonuses, commissions, rental income and more.

From there, the guidelines allow certain deductions to reach each parent's adjusted income, such as:

• Court-ordered support actually paid for other children or a former spouse
• Half of self-employment tax actually paid
• Mandatory (not voluntary) retirement contributions
• State income taxes actually paid

If a parent is voluntarily unemployed or underemployed, the court can base support on what that parent could reasonably earn rather than what they choose to earn.

Step 2: Apply the guideline percentage

Under RSA 458-C:3, the percentage depends on two things: the number of children and the parents' combined net income. The percentage gets somewhat lower as combined income goes up. As a general range under the current table:

The exact percentage for your family comes from the official table and worksheet. Small differences in how income is counted can change the result meaningfully.

Step 3: Divide it between the parents

Here is a simplified example. Say Parent A earns 60% of the combined income and Parent B earns 40%, and the guideline total for their child works out to $1,500 a month. Parent A's share is $900 and Parent B's share is $600. If the child lives primarily with Parent B, Parent A would generally pay Parent B about $900 a month.

This example is for illustration only. Real calculations use the official worksheet and account for taxes, deductions and other adjustments.

What about shared or 50/50 parenting time?

Parenting time matters. RSA 458-C:5 lists "special circumstances" that can justify adjusting the guideline amount, including shared parenting schedules. In general terms:

• When parents have approximately equal parenting time (each more than 40% of the schedule) and substantially similar incomes (within about 10% of each other), the law presumes a support order of zero is appropriate, though that presumption can be challenged.
• When parenting time is substantially shared (each more than 35%) and incomes are substantially similar, a deviation from the guideline amount is presumed appropriate.
• When incomes are dissimilar, the guideline amount is generally presumed correct, and with a shared schedule the court looks at the children's best interests, including whether the lower-earning parent can meet their costs. In shared schedules without extraordinary circumstances, support generally should not leave the receiving parent with a higher adjusted monthly income than the paying parent.

These rules, which were updated effective 2025, have specific definitions and exceptions, so whether they apply to your schedule is worth reviewing carefully.

Other reasons the court may deviate

The court can also adjust support for other special circumstances, such as a child's significant medical or educational needs, unusually high or low incomes, or the costs of parenting time when parents live far apart. Health insurance and child care costs are also addressed in the order.

Can child support be changed later?

Yes. Under RSA 458-C:7, either parent can generally ask for a review three years after the last support order, even without a major change. A substantial change in circumstances, such as a significant change in income, can justify a review sooner. Until the court changes the order, the existing order stays in effect, and informal agreements to pay less are generally not enforceable.

The bottom line

New Hampshire child support follows a formula, but applying it correctly depends on how income is defined, what deductions apply and whether any special circumstances fit your family. Getting those details right at the start matters, because the order will shape your finances for years.

This article is for general informational purposes only and does not constitute legal advice. Laws change, and how they apply depends on the specific facts of your case. Reading this article or contacting Granfield Legal Services does not create an attorney-client relationship. Attorney advertising.