Child support in the United States is calculated using one of three guideline formulas adopted at the state level. Federal law (42 U.S.C. §667) requires every state to publish numeric guidelines, but Washington intentionally left the math to each state. The result is a patchwork: a parent who earns $5,000/month in Texas will owe a very different amount than the same parent in California or New York. This guide walks through all three formulas, the inputs that matter, and what makes a guideline result move up or down in court.
The three guideline models
Every state uses one of three guideline frameworks. Knowing which one applies to you is the first step in understanding what you might owe.
| Model | How it works | Examples |
|---|---|---|
| Income Shares | Combines both parents' incomes, applies a state schedule, then splits proportionally. | CA, FL, NY, IL, PA, OH, GA, NC, MI |
| Percentage of Income | Flat percentage of the obligor's income, scaling with the number of children. | TX, MS, AK, AR, NV, ND, WI |
| Melson | Hybrid that protects each parent's self-support reserve before allocating support. | DE, HI, MT |
How Income Shares works in practice
The Income Shares model assumes that both parents would have spent a certain percentage of their combined income on the children if they lived together. The state publishes a schedule showing the basic obligation at each income level.
Example walkthrough:
- Parent A earns $5,000/month gross. Parent B earns $3,000/month gross. Combined: $8,000.
- The state schedule sets the basic obligation for one child at this income level at roughly $1,400.
- Parent A earns 62.5% of combined income, so Parent A's pro-rata share is about $875.
- If Parent A is the non-custodial parent, Parent A pays $875/month to Parent B.
- Add-ons for childcare ($300/mo) and health insurance ($200/mo) are split 62.5/37.5.
How Percentage of Income works
Texas is the textbook example. Take the obligor's net resources (gross income minus a standardized federal tax estimate, Social Security, Medicare, and the children's health insurance), then multiply by a fixed percentage.
- 1 child → 20% of net resources
- 2 children → 25%
- 3 children → 30%
- 4 children → 35%
- 5 or more → at least 40%
What every formula needs from you
Regardless of which state you live in, you'll need to provide the same core inputs:
- Gross monthly income from all sources — wages, self-employment, bonuses, commissions, rental income, and most government benefits.
- Number of children covered by the order. Children from prior relationships may qualify for separate adjustments.
- Custody arrangement — primary, joint, or shared physical custody, measured in overnights per year.
- Health insurance and childcare costs that are reasonable and work-related.
- Other support obligations the obligor is legally paying for prior children.
What can move a result outside the guideline?
Courts can deviate from the guideline result with written findings. Common reasons include a child's documented special needs, private-school tuition that both parents previously agreed to, extraordinary medical costs, very high combined incomes that exceed the published schedule, and demonstrated bad-faith underemployment by either parent.
Try our free child support calculator for an instant estimate, or pick your state directly: California, Texas, or Florida.
Frequently Asked Questions
Which states use the Income Shares model?
About 41 US states use Income Shares, including California, Florida, New York, Illinois, Pennsylvania, Ohio, Georgia, North Carolina, and Michigan. The model treats children as entitled to the same share of family income they would have received in an intact household.
Which states use the Percentage of Income model?
Texas, Mississippi, Alaska, Arkansas, Nevada, North Dakota, and Wisconsin use a flat-percentage formula. The non-custodial parent pays a fixed share of net income that scales with the number of children.
Why does the same income produce different support amounts in different states?
Each state writes its own guideline tables, low-income reserves, parenting-time adjustments, and add-ons for childcare and health insurance. Two parents earning identical paychecks can owe very different amounts depending on their state.
Can the calculator predict the exact amount a judge will order?
No. Calculators show a guideline estimate, but judges can deviate when the result would be unjust. Special needs, extraordinary educational expenses, and high-asset cases routinely move outside the guideline.
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