How Child Support Calculator Works
Our free child support calculator estimates monthly payments using the actual formula your state uses. Unlike generic calculators that apply one formula to all states, this tool models the three distinct calculation methods used across the US: Income Shares, Percentage of Income, and the Melson Formula.
Most states (about 40) use the Income Shares model, which combines both parents' incomes, looks up the total child-rearing cost for that income level and number of children, then splits the obligation proportionally based on each parent's share of combined income. The non-custodial parent pays their share to the custodial parent.
Texas, Wisconsin, and a few other states use the simpler Percentage of Income model, which bases support on the non-custodial parent's income alone — typically 20% for one child, 25% for two, 30% for three, and so on.
Delaware uses the Melson Formula, which first ensures both parents can meet their own basic needs, then calculates support based on remaining income.
You enter both parents' gross monthly income, number of children, custody split (percentage of overnights), childcare costs, and health insurance premiums for the children. The calculator applies your state's specific formula and adjustments, including the custody time offset that most states apply when the non-custodial parent has significant parenting time.
For the full financial picture during separation, use the Alimony / Spousal Support Calculator alongside this tool, and the Free Budgeting App to plan your post-separation finances.
Key Terms Explained
- Income Shares Model
- The most common child support model (40+ states) that bases the obligation on both parents' combined income and splits it proportionally.
- Percentage of Income Model
- A simpler model (TX, WI, and others) that calculates support as a percentage of only the non-custodial parent's income.
- Custodial Parent
- The parent with whom the child primarily resides — typically the parent with more than 50% of overnights.
- Parenting Time Adjustment
- A reduction in child support when the non-custodial parent has significant overnight time (usually 20%+ of overnights), recognizing they bear direct costs during that time.
- Imputed Income
- Income assigned by the court to a voluntarily unemployed or underemployed parent, based on their earning capacity — prevents intentional income reduction to lower support.
- Deviation Factors
- Circumstances that allow a court to set support above or below the guideline amount: special needs, travel costs, extraordinary medical expenses, or other children.
Who Needs This Tool
Wants to understand expected child support obligations before meeting with an attorney, to budget for post-divorce life and make informed custody negotiation decisions.
Currently paying child support and wants to verify the amount aligns with state guidelines, especially after a change in income or custody arrangement.
Needs a quick estimate during mediation sessions to help both parties understand the likely court-ordered amount before finalizing their agreement.
Exploring a move to another state and wants to compare how different state formulas would affect their support obligation or receipt.
Methodology & Formulas
Income Shares: Combined Gross Income → lookup Basic Child Support Obligation (BCSO) by income level and number of children → each parent's share = their income / combined income × BCSO → adjusted for custody time (deviation typically starts at 20%+ overnights) → add childcare and health insurance costs split proportionally. Percentage of Income: Non-custodial parent's gross income × percentage (varies by state and number of children). Custody offset reduces obligation proportionally to overnights above threshold.
Pro Tips
- Child support guidelines produce an estimate — courts can deviate up or down based on special circumstances, so treat this as a starting point for planning.
- If you have significant parenting time (110+ overnights/year), make sure to input accurate overnight counts — this can reduce support obligations by 20-40%.
- Include ALL income sources when calculating — courts consider bonuses, commissions, rental income, and investment income, not just W-2 wages.
- Childcare and health insurance costs for the children are typically added on top of the base support amount and split between parents.
- Child support is not tax-deductible for the payer and not taxable income for the recipient — unlike alimony for pre-2019 divorce agreements.