Disposable income for child support is what remains of a parent’s gross income after subtracting a short, specific list of mandatory deductions: federal, state, and local income taxes; Social Security and Medicare taxes; health insurance premiums for the parent and covered children; mandatory retirement contributions; mandatory union dues; and any pre-existing court-ordered child support or alimony. That figure — sometimes called “net income” in the guidelines — is the number each state plugs into its child support formula. It is narrower than your take-home pay and narrower than taxable income, because only deductions you cannot avoid count.
Where the Calculation Starts: Gross Income
Courts define gross income broadly. Wages and salary are the obvious pieces, but the list runs much further. Commissions, bonuses, tips, overtime, and self-employment earnings all count. So do dividends, interest, rental income, pensions, annuities, and Social Security retirement or disability benefits. Workers’ compensation, unemployment insurance, and even lottery or prize winnings generally go in. If money comes in, most states treat it as income whether or not it appears on a tax return.
Self-employment income gets a closer look. The gross figure is revenue minus legitimate business expenses, and courts tend to scrutinize those expenses carefully. Deductions for personal use of a business vehicle, or above-market pay to family members on the payroll, are common targets for disallowance. What survives that review is what feeds the formula.
Income That Usually Does Not Count
A few sources are excluded in most states. The most important is Supplemental Security Income (SSI). Because SSI is a need-based federal benefit rather than an earned entitlement, it is generally not counted. Social Security Disability Insurance (SSDI) is different — it replaces wages the parent previously earned, so it is counted.
A new spouse’s income is another common source of confusion. Remarrying does not automatically pull your new partner’s paycheck into the calculation. Most states exclude it from the formula, though a court may consider it indirectly if the new spouse’s contributions free up more of the parent’s own income for discretionary spending. Public assistance benefits like Temporary Assistance for Needy Families (TANF) and foster care payments are also typically excluded.
The Deductions That Produce Disposable Income
Once gross income is established, specific deductions come off. These are narrower than what you might claim on a tax return, and they reflect costs that genuinely reduce the cash a parent has available.
- Federal, state, and local income taxes. Actual withholding, or in some states the tax liability calculated at the correct filing status and number of exemptions.
- Social Security and Medicare taxes. The employee share of FICA — 6.2% for Social Security and 1.45% for Medicare. Self-employed parents pay both halves, so their FICA deduction is larger.
- Health insurance premiums. The cost of coverage for the parent and any children under a support obligation. Some states cap how much of a premium qualifies as reasonable.
- Mandatory retirement contributions. Only contributions required as a condition of employment, such as a public pension plan you cannot opt out of. Voluntary 401(k) contributions usually do not qualify.
- Mandatory union dues. Dues required to keep your job are deductible. Voluntary professional association fees are not.
- Prior support obligations. Court-ordered child support or alimony already being paid for other children or a former spouse is subtracted so you are not counted twice on the same dollars.
The pattern is straightforward. If you have no choice about paying it, it probably reduces your disposable income. If it is voluntary, it probably does not.
How Prior Alimony Complicates the Math
Pre-existing alimony obligations come off gross income, but the tax treatment matters. For divorce agreements finalized before 2019, the person paying alimony can deduct those payments on their federal return, which lowers taxable income and therefore lowers the income tax deduction in the child support formula. For agreements finalized after December 31, 2018, the payer can no longer deduct alimony federally. The payer’s taxable income is higher, the tax bill is bigger, and that bigger tax bill then becomes a bigger deduction from gross income when calculating disposable income. The net effect is complicated enough that two parents with identical salaries and identical alimony payments can end up with different disposable income figures based solely on when their divorces were finalized.1Internal Revenue Service. Alimony, Child Support, Court Awards, Damages
How the Number Feeds the Support Formula
Once each parent’s disposable income is calculated, the state guideline takes over. Roughly 41 states use the income shares model. This approach adds both parents’ disposable incomes together to estimate what the household would have spent on the child if the parents still lived together, then splits that obligation in proportion to each parent’s share of the combined total. If one parent earns 60% of the combined figure, that parent is responsible for 60% of the support obligation.
A handful of states use a percentage-of-income model, which applies a set percentage only to the noncustodial parent’s income. Some apply a flat percentage regardless of income level; others use a sliding scale where the percentage decreases as income rises. The same disposable income figure can produce noticeably different support amounts depending on which model your state uses.
Federal regulations require every state to review its guidelines at least once every four years, considering economic data on the cost of raising children, local labor market conditions, and the impact on families with incomes below 200% of the federal poverty level.2eCFR. 45 CFR 302.56 – Guidelines for Setting Child Support Orders
When Courts Use a Different Income Number
Your actual paystub is not always the end of the story. A parent who quits a well-paying job to work part-time or stops working altogether will not automatically see their obligation drop. If a court finds the reduced income is deliberate — motivated by a desire to shrink support rather than a legitimate reason like disability, caregiving for a young child, or pursuing education — the court can impute income. That means calculating support based on what the parent could be earning rather than what they actually earn.
Courts look at recent work history, education and vocational training, occupational qualifications, and prevailing wages in the local job market. A parent with no recent work history and no specialized skills may have income imputed at minimum wage for a 40-hour week. A parent who recently left a six-figure career will face a much higher imputed figure. Motive is the pivotal question. A parent who takes a pay cut to change careers in good faith, or who loses a job through no fault of their own, is in a very different position than one who walks away from steady employment right before a support hearing.
Variable and Irregular Income
Not everyone earns the same amount each month. Parents who rely on commissions, seasonal work, bonuses, or overtime present a challenge because their income fluctuates. Courts handle this by averaging income over a representative period, typically two to three years of tax returns. The goal is a stable monthly figure that reflects the parent’s real earning pattern rather than an unusually good or bad month.
One-time events are treated differently. A signing bonus, an inheritance, or litigation settlement proceeds may be prorated over a period or handled separately from the base calculation. Some states allow the court to order a percentage of non-recurring income as a supplemental payment on top of the regular monthly amount. Equity compensation like restricted stock units raises similar questions; RSUs are typically counted as income when they vest, not when they are granted.
A Separate “Disposable Earnings” Rule for Garnishment
There is a second, unrelated concept with a nearly identical name, and the two get confused constantly. Under the federal Consumer Credit Protection Act, “disposable earnings” is the portion of a worker’s pay remaining after amounts required by law to be withheld, such as taxes and Social Security.3Legal Information Institute at Cornell Law. 15 USC 1672(b) – Definition of Disposable Earnings This figure is not used to calculate how much support you owe. It sets a ceiling on how much of your paycheck can actually be garnished to collect the support you already owe.
The federal caps are:4Office of the Law Revision Counsel. 15 USC 1673 – Restriction on Garnishment
- 50% of disposable earnings if the parent is also supporting a current spouse or another child.
- 60% of disposable earnings if the parent is not supporting anyone else.
- An additional 5% on top of either limit if the parent is more than 12 weeks behind, bringing the caps to 55% and 65%.
These caps are a ceiling, not a target. The actual order may be well below them. But if a parent’s combined obligations from multiple orders ever exceed the cap, garnishment is limited to the federal maximum. This is where the two “disposable” concepts trip people up: you can owe more than your employer is allowed to withhold, which means arrears can accumulate even with an active wage garnishment already running.