Family Law & Divorce · Haute Lawyer Network
How Is Child Support Calculated?
Last reviewed: October 2026 · Jurisdiction: United States (example: Florida)
Every state sets child support with a guideline formula that federal law requires. Most use an income shares model, which combines both parents' incomes and splits the obligation by each parent's share; others use a percentage of the paying parent's income. Overnights, health insurance and child care adjust the result, and judges can deviate with written reasons.
| Key facts (United States, with Florida as the worked example, as of October 2026) | Rule | Source |
|---|---|---|
| Every state must have guidelines | The guideline amount is a rebuttable presumption; deviating requires a written or on-the-record finding | 42 U.S.C. § 667 · 45 CFR 302.56 |
| States must review their guidelines | At least once every four years | 45 CFR 302.56 |
| Which model states use | Income shares: 41 states, Guam and the U.S. Virgin Islands; percentage of income: 6 states; Melson formula: 3 states; D.C.: hybrid | NCSL: Child support guideline models |
| Florida: model and schedule | Income shares, using a statutory schedule of combined net income and number of children | Fla. Stat. § 61.30 |
| Florida: shared time-sharing | If each parent has at least 20% of overnights, a substantial-time-sharing formula applies (each parent's share × 1.5, weighted by the other parent's overnights) | Fla. Stat. § 61.30(11)(b) |
| Florida: deviating | A court may move more than 5% from the guideline amount only with a written finding explaining why the guideline amount would be unjust or inappropriate | Fla. Stat. § 61.30(1)(a) |
The three guideline models
| Model | How it works | Used by (per NCSL) |
|---|---|---|
| Income shares | Combine both parents' incomes, look up the total support for that income and number of children, then split it by each parent's share of the combined income | Most states, including Florida, California and New York |
| Percentage of income | A percentage of the paying parent's income only, either flat or varying by income level | Alaska, Mississippi, Nevada, North Dakota, Texas, Wisconsin |
| Melson formula | Income shares plus a self-support reserve for each parent and a standard-of-living adjustment | Delaware, Hawaii, Montana |
How the calculation works: income shares, step by step
- Figure each parent's income. Usually wages, bonuses, commissions, self-employment, rental and investment income, minus items the state allows (such as taxes and mandatory retirement). A court can impute income to a parent who is voluntarily unemployed or underemployed.
- Add the two incomes and find the basic obligation for that combined income and number of children in the state's schedule.
- Split it by percentage. If one parent earns 60% of the combined income, that parent's share is 60% of the basic obligation.
- Add health insurance, uninsured medical costs and work-related child care, usually split in the same proportion.
- Adjust for parenting time. Many states reduce support once the paying parent has a set share of overnights. The threshold varies widely: Florida's is 20% of overnights for each parent.
- Credit other obligations, such as support already being paid for children from another relationship, if the state allows it.
The result is the presumptive amount. A judge can deviate from it, but only with a stated reason.
When support can change
Either parent can ask the court to modify support after a substantial change in circumstances, such as a significant change in income, a new time-sharing schedule or a change in the child's needs. Each state sets its own threshold.
Talk to a family law attorney
- Find a Family Law Attorney · Florida · Miami
- Gerald Kornreich — Miami, family law, Kornreich & Associates
- Lynette Silon-Laguna — Tampa, family law, All Family Law Group, P.A.
Related reading: How is child custody decided? · How do I modify a custody order? · What is interstate custody?
This article is general information, not legal advice, and doesn't create an attorney-client relationship. Child support rules and schedules differ by state. Use your state's official guideline worksheet and talk to a licensed family law attorney.
Sources
Frequently Asked Questions
How is child support calculated if parents share custody equally?
It depends on the state's formula. In income shares states, each parent's share of the obligation is usually calculated and the amounts are offset, so the higher earner often still pays something. In Florida, once each parent has at least 20% of overnights, a substantial-time-sharing formula applies (Fla. Stat. § 61.30(11)(b)).
Can a judge order a different amount than the guidelines?
Yes, but the guideline amount is presumed correct. Federal law requires states to make that presumption rebuttable only with a written or on-the-record finding that the amount would be unjust or inappropriate. Florida requires that finding for any deviation over 5%.
Does child support cover college?
Usually not by default. In most states court-ordered support ends at adulthood or high school graduation. Some states let courts order help with college, and parents can agree to it in a settlement.
How long does child support last?
It's set by state law. In Florida, support generally lasts until the child turns 18, or until high school graduation if the child is expected to graduate before turning 19 (Fla. Stat. § 61.13(1)(a)). Many states allow support beyond the age of majority for a child with a disability who can't become self-supporting.
Can a parent refuse visitation if support isn't paid?
No. Support and parenting time are legally separate. The remedy for unpaid support is enforcement through the court or the state child support agency, not withholding the child.
What if a parent hides income?
Courts can use financial discovery and subpoenas to find it, and can impute income based on earning capacity. Hiding income can also lead to sanctions.
How often do child support guidelines change?
Federal rules require each state to review its guidelines at least every four years (45 CFR 302.56), so schedules and formulas are updated periodically. Check the version in effect when your case is decided.
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