Child Support Calculator - Free Online Tool

Estimate monthly child support using the Income Shares Model

Child support is a court-ordered financial contribution from one parent to the other to help cover the costs of raising a child. When parents separate or divorce, a child support order ensures that both parents continue to share financial responsibility for their children proportionally to their incomes and time. This calculator uses the Income Shares Model — the approach used by approximately 40 U.S. states — to give you a reliable estimate of what monthly child support might look like in your situation. The Income Shares Model works on a straightforward principle: children should receive the same proportion of parental income they would have enjoyed if both parents lived together. Instead of placing the entire burden on one parent, the model looks at both parents' combined gross monthly incomes and uses a guideline percentage table to determine a base obligation. That base is then split proportionally based on each parent's share of the combined income. Understanding the key inputs is the first step. Both parents' gross monthly income — meaning before taxes and deductions — must be reported. This includes wages, salary, commissions, bonuses, overtime pay, self-employment income, rental income, investment returns, pension distributions, and disability payments. The number of children covered by the order and the parenting time arrangement are equally critical: each additional child increases the guideline percentage, and a non-custodial parent who has the child for 40% or more of overnights per year (roughly 146+ nights) may qualify for a shared parenting adjustment that reduces the net obligation. Beyond the base obligation, two major add-on costs are shared proportionally: monthly child care expenses (daycare, after-school programs) and the health insurance premium attributable to the children. These are added to each parent's base share, so the final net payment reflects who actually incurs which expenses. For most families, these add-ons represent a meaningful portion of the total obligation — often 20 to 30 percent above the base guideline amount. This calculator also includes an advanced section for families with more complex finances: prior child support orders for children from other relationships, spousal maintenance (alimony) payments, and extraordinary medical expenses. Under the Income Shares Model, existing support orders for other children and spousal maintenance you currently pay are deducted from your gross income before the calculation — giving you an adjusted income that more accurately reflects available resources for the children in question. The results include a parenting time sensitivity analysis showing how the estimated monthly payment changes across the full range of custody arrangements (0% to 50%), a visual income share donut chart, and a component breakdown showing base support, child care, and health insurance as separate bars. A step-by-step calculation walkthrough is also provided so you can follow the math and verify the result. Important notes about this estimate: child support laws vary significantly by state. Some states — including Wisconsin and Texas — use a Percentage of Income model instead, which only considers the non-custodial parent's income. Other states use complex lookup tables that vary by exact income level, and many have special rules for very low-income parents or high-income households. This calculator applies general Income Shares principles and is best used to understand the likely range and logic of your obligation, not as a definitive legal calculation. For a court-ready figure, you should always work with a licensed family law attorney in your state.

Understanding Child Support Calculations

What Is Child Support?

Child support is a recurring payment ordered by a court to help cover a child's living expenses after parents separate, divorce, or were never married. It typically covers food, housing, clothing, education, medical care, and other day-to-day costs. Under U.S. law, both parents have a legal obligation to financially support their children, regardless of the custody arrangement. The court determines the amount based on state guidelines, the incomes of both parents, the number of children, parenting time, and any special needs or extraordinary expenses. Support typically continues until the child turns 18 or, in some states, until graduation from high school if the child is still a minor. Under the Tax Cuts and Jobs Act of 2017, child support is neither tax-deductible for the paying parent nor taxable income for the receiving parent.

How Is Child Support Calculated?

Most U.S. states use the Income Shares Model, which starts with both parents' adjusted gross monthly incomes. A guideline percentage — ranging from 20% for one child to 50% for six children — is applied to the combined income to determine the total base obligation. Each parent's share of that obligation is proportional to their share of combined income. For example, if Parent 1 earns 60% of combined income, they owe 60% of the base obligation. This base is then adjusted for parenting time: when the non-custodial parent has 146 or more overnights per year (40%+), a shared parenting formula applies that multiplies the base by 1.5 and nets out each parent's credit for time spent. Child care costs and health insurance premiums are added proportionally on top of the base obligation. Prior support orders for other children and spousal maintenance paid are deducted before calculating income shares.

Why Parenting Time Matters

Parenting time directly affects the child support calculation in two important ways. First, the parenting arrangement determines who is the 'obligor' (paying parent) — generally the parent who spends less time with the child. Second, when the paying parent's time reaches the 40% threshold (approximately 146 overnights per year), the formula switches from a standard custody model to a shared parenting model. The shared parenting formula multiplies the base obligation by 1.5 before splitting it, recognizing that both parents are maintaining separate households equipped for the child. This can meaningfully reduce the net payment. The sensitivity chart in this calculator shows exactly how the obligation changes as parenting time increases from 0% to 50%, helping both parents understand the financial implications of different custody arrangements.

Important Limitations

This calculator applies general Income Shares Model principles and is intended as an educational estimate only. Actual child support orders differ based on state-specific guidelines, income lookup tables, and judicial discretion. States such as Wisconsin, Texas, and Alaska use a Percentage of Income model that considers only the non-custodial parent's income. Income definitions vary — some states include imputed income for voluntarily unemployed parents, gifts, or inheritances. Courts have discretion to deviate from guidelines when the presumptive amount would be unjust or inappropriate. Special circumstances including disabled children, extraordinary educational needs, split custody of multiple children, and self-employment income require specialized analysis. This tool does not account for state tax withholding, self-employment tax adjustments, or statutory income caps. Always consult a licensed family law attorney in your state for a calculation that will hold up in court.

Child Support Formulas

Combined Adjusted Income

Combined Income = (Parent 1 Gross − Prior Support − Alimony) + (Parent 2 Gross − Prior Support − Alimony)

Both parents' gross monthly incomes are reduced by existing court-ordered child support for other children and any spousal maintenance paid, then summed to determine the combined adjusted income used as the calculation base.

Base Guideline Obligation

Base Obligation = Combined Income × Guideline Percentage

A state guideline percentage (typically 20% for 1 child, 25% for 2, 30% for 3, 35% for 4, 40% for 5, 50% for 6) is applied to the combined adjusted income to determine the total base child support obligation.

Each Parent's Share

Parent Share = Base Obligation × (Parent Income ÷ Combined Income)

The base obligation is split proportionally based on each parent's share of the combined adjusted income. If Parent 1 earns 60% of combined income, they are responsible for 60% of the base obligation.

Shared Parenting Adjustment

Adjusted Base = Base Obligation × 1.5; Net Payment = (Other Parent's Share × 1.5) − (Paying Parent's Share × 1.5) × Time Fraction

When the non-custodial parent has 40% or more parenting time (146+ overnights/year), the base is multiplied by 1.5 and each parent's obligation is offset by their time credit, reducing the net payment.

Reference Tables

Income Shares Guideline Percentages by Number of Children

Typical guideline percentages used in the Income Shares Model. Actual percentages vary by state and may use detailed lookup tables based on exact combined income levels.

Number of Children	Guideline % of Combined Income	Example at $8,000 Combined
1 child	20%	$1,600/mo
2 children	25%	$2,000/mo
3 children	30%	$2,400/mo
4 children	35%	$2,800/mo
5 children	40%	$3,200/mo
6 children	50%	$4,000/mo

Child Support Calculation Models by State Approach

U.S. states use one of three primary models. The Income Shares Model is most common (~40 states), while a few states use Percentage of Income or the Melson Formula.

Model	States Using	Key Feature
Income Shares	~40 states (CA, NY, FL, IL, PA, etc.)	Both parents' incomes considered; obligation split proportionally
Percentage of Income	TX, WI, AK, MS, ND, NV	Only non-custodial parent's income used; flat % applied
Melson Formula	DE, HI, MT	Income Shares variant with self-support allowance deducted first

Worked Examples

Two Children — Standard Custody

Parent 1 earns $5,000/mo gross, Parent 2 earns $3,000/mo gross. Two children. Parent 1 has 20% parenting time (73 overnights). Monthly childcare: $400. Health insurance: $200. No prior support or alimony.

Combined adjusted income: $5,000 + $3,000 = $8,000/mo

Guideline percentage for 2 children: 25%

Base obligation: $8,000 × 0.25 = $2,000/mo

Parent 1 income share: $5,000 ÷ $8,000 = 62.5%

Parent 1 base share: $2,000 × 0.625 = $1,250

Add-on share (childcare + insurance): ($400 + $200) × 0.625 = $375

Total Parent 1 obligation: $1,250 + $375 = $1,625/mo

Parent 1 pays approximately $1,625 per month in child support under the standard custody formula.

Two Children — Shared Parenting Adjustment

Same incomes as above ($5,000 and $3,000), but Parent 1 now has 45% parenting time (164 overnights/year), triggering the shared parenting formula.

Combined adjusted income: $8,000/mo. Base obligation: $2,000/mo

Shared parenting multiplier: $2,000 × 1.5 = $3,000 adjusted base

Parent 1 share: $3,000 × 0.625 = $1,875

Parent 2 share: $3,000 × 0.375 = $1,125

Parent 1 time credit: $1,875 × 0.45 = $843.75

Parent 2 time credit: $1,125 × 0.55 = $618.75

Net payment: ($1,875 − $843.75) − ($1,125 − $618.75) = $1,031.25 − $506.25 = $525

Under shared parenting (45% time), Parent 1's net monthly payment drops to approximately $525 — significantly less than the $1,625 under standard custody.

How to Use the Child Support Calculator

Enter Both Parents' Gross Monthly Income

Input each parent's total gross monthly income before taxes — including wages, bonuses, self-employment earnings, investment returns, and rental income. Be as accurate as possible: the income split directly determines each parent's share of the obligation.

Set the Number of Children and Parenting Time

Select how many children are covered by this support order. Then use the slider to set the paying parent's percentage of parenting time (overnights per year). Reaching 40% — about 146 overnights — triggers the shared parenting formula, which can significantly reduce the net payment.

Add Shared Expenses

Enter monthly child care costs (daycare, after-school programs) and the children's health insurance premium. These are added proportionally to each parent's base obligation. For more complex situations, expand the Advanced Inputs to add prior support orders, alimony, and extraordinary medical expenses.

Review Results and Sensitivity Analysis

The results show your estimated monthly and annual payment, income share split, obligation component breakdown, and a sensitivity chart showing how the payment changes across parenting time percentages. Use Export CSV to save results or Print to create a paper record for your attorney consultation.

Perguntas Frequentes

What is the Income Shares Model?

The Income Shares Model is a child support calculation approach used by approximately 40 U.S. states. It starts with the principle that children should receive the same proportion of parental income they would have had if both parents lived together. The model adds both parents' gross monthly incomes, applies a state guideline percentage based on the number of children, and then allocates the resulting base obligation to each parent proportionally based on their share of combined income. This means both parents contribute according to their financial capacity, rather than the entire burden falling on one parent. Child care costs and health insurance premiums are then split proportionally and added to the base obligation to arrive at the net monthly payment.

What triggers the shared parenting formula?

The shared parenting formula is triggered when the paying parent (non-custodial parent) has 146 or more overnights per year with the child — equivalent to approximately 40% of the year. When this threshold is reached, the base obligation is multiplied by 1.5 before being split. This multiplier recognizes that both parents must maintain separate households equipped for the child, resulting in higher combined household costs. The formula then nets out each parent's obligation based on the other parent's time, which typically results in a lower net payment than the standard formula. The sensitivity chart in this calculator shows the exact breakpoint where this shift occurs.

What counts as gross income for child support?

Gross income for child support purposes is broadly defined and includes: wages and salary, overtime and bonuses, commissions and tips, self-employment income (revenue minus ordinary/necessary business expenses), rental income, investment dividends and capital gains, pension and retirement distributions, Social Security and disability benefits, workers' compensation, unemployment benefits, and income from trusts or inheritances. Courts can also impute income to a parent who is voluntarily unemployed or underemployed, assigning what the parent could be earning based on their education, work history, and the local job market. Gifts and in-kind income from a new partner's household may also be considered in some jurisdictions.

How does prior child support for other children affect the calculation?

Under the Income Shares Model, child support orders you are currently paying for children from a prior relationship are deducted from your gross income before calculating your income share for the current order. This adjusted income — sometimes called 'net income' or 'adjusted gross income' — is the figure used to determine your proportional share of the combined obligation. The logic is that income already legally committed to other children should not be double-counted for a new support order. Spousal maintenance (alimony) you are currently paying is similarly deductible. However, voluntary payments or informal support arrangements that are not court-ordered may not qualify for this deduction.

Can child support be modified after it is set?

Yes. Child support orders are modifiable when there is a substantial change in circumstances. Under most state guidelines, you can request a modification every three years without needing to show a change — the court will review the order at that point. Outside of the three-year window, you generally need to demonstrate a significant change, such as a 15% or greater change in either parent's income, a job loss, a major change in parenting time, a significant change in the child's needs (such as a new medical diagnosis), or one parent gaining or losing a child from another relationship. Modifications are not automatic — you must file a petition with the court. The order remains in effect as-is until a new order is entered.

How is child support typically enforced?

Once a child support order is entered by the court, enforcement mechanisms are strong. The most common tool is an income withholding order (wage garnishment), which automatically deducts support payments from the paying parent's paycheck and remits them to the state disbursement unit. Other enforcement tools include interception of state and federal tax refunds, suspension of driver's licenses and professional licenses, denial of passport applications, reporting to credit bureaus, contempt of court proceedings (which can result in fines or jail time), and placing liens on property. Failure to pay child support can become a federal crime if amounts are large enough and the parent crosses state lines to avoid payment.