Glossary

Key terms

Timeshare: How much time each parent spends with the children. Usually measured in overnights per month.; The high earner's approximate percentage of primary physical responsibility for the children (H%). Derived from overnights per month (out of 30).
Net disposable income: Money you have left after paying taxes and required deductions.; Per §4059: Gross income minus federal income tax, CA state tax, FICA/SE tax, CA SDI, and §4059(c)–(g) direct deductions.
Gross income: All the money you earn before taxes are taken out.; Per §4058: All income from any source including wages, self-employment, interest, dividends, capital gains, rental, retirement, Social Security, unemployment, and workers comp. Public assistance (TANF, SSI) excluded per §4058(c).
Low-Income Adjustment (LIA): A rule that may lower child support if the paying parent doesn't earn much money.; Per §4055(b)(7): Rebuttable presumption of reduced support when the monthly net of the parent paying support is below full-time minimum wage gross ($2,929 for 2026). Reduction formula: CS × (threshold − net) / threshold.

EITC: A tax credit for people who work but don't earn a lot. It can give you money back.; Earned Income Tax Credit: Federal refundable credit phased in, plateaus, and phases out based on earned income and filing status.
CTC: A tax credit for having children. Worth up to $2,200 per child in 2025.; Child Tax Credit: For 2025 (post-OBBBA), $2,200 per qualifying child under age 17.
CalEITC: California's version of the federal EITC. Extra money back if you qualify.; California Earned Income Tax Credit: State refundable credit with a hard income ceiling of $31,950.
YCTC: California credit for parents with young children (under 6). Worth $1,154 per child.; Young Child Tax Credit: California refundable credit of $1,154 per dependent under age 6.

FICA: Money taken from your paycheck for Social Security and Medicare. About 7.65% of your pay.; Federal Insurance Contributions Act: 6.2% Social Security on wages up to $176,100 (2025), plus 1.45% Medicare on all wages, plus 0.9% Additional Medicare above filing-status threshold.
SDI: California disability insurance taken from your paycheck. About 1.2% of your pay.; California State Disability Insurance: 1.2% for 2025, 1.3% for 2026, no wage cap since SB 951.
Self-employment tax: If you work for yourself, you pay both the employee and employer share of Social Security and Medicare.; Per IRC §1401: Combined employee and employer portion of SS/Medicare for self-employed. Computed as 15.3% × 92.35% of net SE earnings.

Childcare add-on: Daycare or babysitting costs so a parent can work or go to school. Split between parents based on income.; Per §4062(a)(1): Mandatory add-on for reasonable childcare costs incurred to work or obtain work-related education/training.
Health care add-on: Out-of-pocket medical costs for the children not covered by insurance.; Per §4062(a)(2): Mandatory add-on for reasonable uninsured health-care costs for the children.

Hardship deduction: If you have unusual expenses (major medical bills, big losses, other children to support), you may qualify for reduced support.; Per §4070: Reductions from net disposable income for extraordinary health expenses, catastrophic loss, or minimum basic living expenses for other natural/adopted children residing with the parent.

Single: Filing status if you're not married and don't qualify for head of household.
Head of Household: Filing status if you're not married, pay more than half the household costs, and have a child living with you more than half the year. Usually gives better tax rates.; Unmarried filer who paid more than half the cost of keeping up a home and had a qualifying dependent living with them for more than half the year.
Married Filing Jointly: Filing status for married couples who file one tax return together.
Married Filing Separately: Filing status for married couples who each file their own tax return.

K multiplier: A number used in the formula that factors in both parents' incomes and time with the children.; Per §4055(b)(3): The income-allocation factor computed from total net monthly income and the high earner's timeshare.
HN: The higher-earning parent's monthly income after taxes.; High earner's net monthly disposable income.
TN: Both parents' combined monthly income after taxes.; Total net monthly disposable income of both parents combined.
Multi-child multiplier: Support goes up for more children, but not by the same amount for each: 2 kids = 1.6×, 3 kids = 2×, and so on.; Per §4055(b)(4): 1 child = 1.0, 2 = 1.6, 3 = 2.0, 4 = 2.3, up to 10 = 2.86.