Child support in New Hampshire is calculated as a percentage of both parents’ combined net income, ranging from about 19% to 25.6% for one child depending on how much the household earns together. The total obligation is then split between the parents in proportion to each parent’s share of that combined income. As a rough anchor: a family with $60,000 in combined annual net income and one child owes roughly $1,100 a month in total support, divided between the parents by income share.
The Guideline Percentages
New Hampshire’s formula lives in RSA 458-C:3. The percentage applied to combined net income drops as income rises, on the theory that higher-earning households spend a smaller fraction of income on basic child-rearing costs.1New Hampshire General Court. New Hampshire Code 458-C:3 – Child Support Formula
- $15,000 or less: 25.6% (1 child), 35.5% (2), 42.5% (3), 45% (4+)
- $25,000: 25%, 35%, 42%, 44.5%
- $35,000: 24%, 33.5%, 40.5%, 43%
- $50,000: 23%, 31.5%, 38%, 40.5%
- $60,000: 22%, 30.5%, 36.5%, 39%
- $70,000: 21.5%, 30%, 36%, 38.5%
- $80,000: 21%, 29%, 35%, 37.5%
- $90,000: 21%, 28.5%, 34.5%, 37%
- $100,000: 20%, 27.5%, 33%, 35.5%
- $125,000 or more: 19%, 26%, 31%, 33.5%
Between two rows, the percentage is interpolated proportionally. The Department of Health and Human Services publishes a detailed schedule in $1,000 increments that does the interpolation for you.
How the Amount Is Split Between Parents
The math has three steps. Add the parents’ adjusted gross incomes together. Multiply that combined figure by the percentage from the table. Then divide the result between the parents by their share of the combined income. The parent with less parenting time pays their share to the other parent.
A worked example makes the split concrete. Parent A earns $4,000 a month; Parent B earns $2,000. Combined monthly income is $6,000, or $72,000 a year. For one child at that income, the interpolated rate is about 21.3%, producing a total monthly obligation of roughly $1,278. Parent A earns two-thirds of the combined income, so Parent A’s share is about $852. Parent B’s share is about $426.
When the custodial parent pays for the children’s childcare or health insurance, those costs come off the custodial parent’s adjusted gross income before the proportional share is figured. The effect is to shift a larger portion of the total to the other parent.
What Counts as Income
Gross income is defined broadly. It includes wages, salary, commissions, tips, self-employment earnings, business profits, bonuses, pensions, annuities, Social Security, trust income, lottery and gambling winnings, interest, dividends, other investment income, net rental income, alimony received, and government benefits like workers’ compensation, veterans’ benefits, unemployment, and disability payments.2New Hampshire General Court. New Hampshire Code 458-C:2 – Definitions
Public assistance is excluded: food stamps, SSI, and general town or county assistance don’t count.
Two wrinkles matter for the number you’ll see. Overtime pay from hourly work is not counted, provided the parent works in a trade that traditionally pays overtime and doesn’t control how their own compensation is structured. And if a parent voluntarily quits or takes a lower-paying job without good reason, the court can impute income at the level that parent could be earning. A new spouse’s income doesn’t count toward the parent’s gross income unless the parent is voluntarily unemployed or underemployed, in which case some of that spouse’s income may be attributed to the parent.
Deductions That Reduce the Income Used in the Formula
Each parent’s gross income is reduced by several categories of deductions before the percentages are applied:
- Child support or alimony already being paid under a court or administrative order
- 50% of actual self-employment tax paid
- Mandatory retirement contributions (voluntary 401(k) deferrals don’t qualify)
- State income taxes actually paid (relevant for parents earning income taxed by other states)
- For the paying parent, amounts actually paid for work-related childcare and the children’s health insurance premiums
Federal income taxes are not on the list. New Hampshire applies the percentages to income before federal tax, which surprises parents who assume take-home pay is the starting point.
The Low-Income Floor
Support cannot push a low-earning parent into poverty. The self-support reserve is set at 115% of the federal poverty guideline for one person, which comes to $1,695 per month under the most recent published figures.3New Hampshire Department of Health and Human Services. 2026 Child Support Guidelines
If the paying parent’s gross income is below the reserve and the court finds no deliberate underemployment, the court sets a minimum order rather than running the full formula. If the parent earns more than the reserve but the full guideline amount would drop them below it, the obligation is cut to the difference between adjusted gross income and the reserve, floored at the minimum order.
Shared or Equal Parenting Time
How the children’s time is split can change the number substantially. The statute sets three presumptions:4New Hampshire General Court. New Hampshire Code 458-C:5 – Adjustments to the Application of Guidelines Under Special Circumstances
- Similar incomes and approximately equal time: a rebuttable presumption of $0 support, provided the parents share childcare costs, uninsured medical expenses, and extracurriculars equally.
- Similar incomes and substantially shared but not equal time: a rebuttable presumption that some deviation from the standard guideline is appropriate.
- Different incomes, without a shared or equal schedule: the standard guideline calculation applies with no presumed deviation.
These are presumptions, not automatic outcomes. Either parent can argue for a different result, and the statute is explicit that equal parenting time “shall not by itself constitute ground for an adjustment.” The court also weighs whether the lower-income parent can maintain a similar standard of living for the children.
When Courts Deviate from the Guideline Amount
The guideline number is presumptive. The court starts there and can adjust up or down when special circumstances make the standard calculation unfair, with its reasoning stated in writing. Recognized grounds include:
- Extraordinary medical, dental, or education expenses, including costs for a child with special needs
- Very high or very low combined income, where the guideline amount either substantially exceeds the child’s reasonable needs or fails to make the best use of limited resources
- Support obligations for stepchildren or other dependents
- Reasonable costs of exercising parenting time, so long as the custodial parent can still meet the children’s needs
- Tax consequences, including which parent claims the child as a dependent and the earned income tax credit
- Disposition of the family home when one parent keeps it for the children’s benefit
Estimating Your Own Number
Rather than running the formula by hand, you can use the state’s online calculator, maintained by the Department of Health and Human Services. It asks for each parent’s gross income, health insurance premiums, childcare costs, and any existing support obligations, and it returns a presumptive amount based on the current guideline table.5New Hampshire Department of Health and Human Services. Child Support Calculator
The output is an estimate. A court may use different numbers if it imputes income to an underemployed parent or finds a deviation is warranted.6New Hampshire Department of Health and Human Services. Child Support Guidelines and Calculator
How Long the Obligation Runs
Support ends automatically when the child turns 18, unless the child is still a full-time student in an elementary or secondary school, a charter school, or an approved home education program. In that case, it continues until graduation or two months after the child turns 19, whichever comes first. No filing is needed to trigger termination.7New Hampshire General Court. New Hampshire Code 461-A:14 – Support
Support also ends earlier if the child marries, joins the armed forces, or is legally emancipated. For a child with disabilities, the court can extend support past 18, but any order entered after July 9, 2013 cannot continue past age 21 or past the point when the child no longer qualifies for special education services. New Hampshire does not require parents to pay for college as part of a child support order.
Modifying the Amount Later
Two paths to a change. You can file at any time by showing a substantial change in circumstances, such as a major income shift, a significant change in the parenting schedule, or a change in the child’s needs. You can also file after three years without needing to show any changed circumstances, and let the court simply recalculate under current incomes.8New Hampshire General Court. New Hampshire Code 458-C:7 – Modification of Order
No modification takes effect before the other parent is served with your petition. Anything that accrued before that date stays at the original amount, and back payments can never be reduced retroactively.