Child Support Calculator
Estimate monthly child support payments using both parents' incomes, number of children, custody split, and healthcare responsibility. Designed for divorce planning and mediation prep.
About this calculator
Child support formulas vary by state, but most share a core income-shares or percentage-of-income approach. This calculator uses: Support = max(0, (payorIncome × (numChildren × 0.17 + (numChildren − 1) × 0.03) × (1 − custodyPercent / 100)) + (payorIncome × 0.05 × healthcarePercentage / 100) − (payeeIncome > payorIncome × 0.5 ? payeeIncome × 0.1 : 0)). The base obligation scales with the number of children and is reduced proportionally by the payor's custody share. A healthcare contribution is added as a percentage of payor income. If the payee earns more than half the payor's income, a modest offset reduces the obligation. The result is floored at zero to prevent negative values.
How to use
Payor income: $5,000/month. Payee income: $2,000/month. 2 children. Payor custody: 20%. Healthcare responsibility: 50%. Step 1 — Base rate: 2 × 0.17 + (2−1) × 0.03 = 0.34 + 0.03 = 0.37. Step 2 — Custody reduction: 1 − 20/100 = 0.80. Step 3 — Base support: $5,000 × 0.37 × 0.80 = $1,480. Step 4 — Healthcare add-on: $5,000 × 0.05 × 50/100 = $125. Step 5 — Payee offset check: $2,000 > $5,000 × 0.5 = $2,500? No, so offset = $0. Total: $1,480 + $125 = $1,605/month.
Frequently asked questions
How does shared custody percentage affect monthly child support payments?
The custody reduction factor (1 − custodyPercent/100) directly scales the base support obligation downward as the payor spends more time with the children. At 0% custody the full base applies; at 50% custody the obligation is halved. This reflects the logic that the payor directly incurs costs — food, housing, activities — during their custodial time. In states with formal shared-parenting guidelines, a similar offset typically kicks in above 30–40% parenting time. Increasing overnights through a custody modification can therefore meaningfully reduce support obligations.
What income is used to calculate child support and does it include bonuses?
Most state guidelines use gross monthly income, which includes wages, salaries, self-employment income, bonuses, commissions, rental income, and some government benefits. Courts routinely impute bonus income based on historical averages if bonuses are regular. One-time windfalls like inheritances are treated differently depending on jurisdiction. If you are self-employed, net business income after legitimate deductions — not revenue — is typically used. Intentional underemployment can lead a judge to impute income at your earning capacity rather than your reported income.
When can child support be modified after the initial court order?
Child support orders can be modified when there is a substantial change in circumstances — typically defined as a 10–15% change in either parent's income, a significant shift in custody time, or a major change in the child's needs such as medical expenses. Most states require a formal petition to the court and won't backdate modifications to before the filing date. Informal agreements between parents to pay less are not legally binding and can result in arrears. Periodic reviews every 2–3 years are common in many jurisdictions even without a major change. Using this calculator after income changes helps you determine whether a modification petition is warranted.