Arizona’s income shares model explained

Arizona calculates child support under the Income Shares Model, which is set out in Arizona Revised Statutes § 25-320 and the Arizona Child Support Guidelines. The idea behind this model is that children should receive the same proportion of parental income they would have received if both parents lived together.

Rather than focusing only on the higher-earning or non-custodial parent, the court combines both parents’ incomes to estimate the total cost of raising the child. That total amount is then divided between the parents based on their respective earnings. This structure is why there is no fixed child support percentage in Arizona.

How Arizona calculates child support

Arizona courts follow a structured, step-by-step process to calculate child support. Although the math may appear complex at first, the steps remain consistent across all cases.

Step 1: Determine each parent’s gross income

The calculation starts by identifying each parent’s gross monthly income. This generally includes wages, salary, overtime, bonuses, commissions, and self-employment income. It can also include rental income, investment income, unemployment benefits, disability payments, and Social Security benefits.

Certain income sources are excluded, including child support received for other children and certain means-tested public benefits. The goal is to capture a realistic picture of each parent’s earning ability.

Step 2: Calculate the combined adjusted gross income

Once each parent’s gross income is determined, the amounts are added together. The court may then subtract allowable deductions, such as spousal maintenance paid or existing child support obligations for other children.

The result is the combined adjusted gross income. This number is critical because it is used to find the basic child support obligation under the Arizona guidelines.

Step 3: Find the basic support obligation

Arizona uses a published Child Support Guidelines Schedule to determine the basic monthly support obligation. The schedule aligns with the parents’ combined income and the number of children.

For example, lower combined incomes result in lower baseline support amounts, while higher combined incomes and more children increase the obligation. This baseline amount represents the estimated cost of supporting the children, excluding other expenses.

Step 4: Add additional expenses

After identifying the basic support obligation, the court adds certain child-related expenses. These commonly include work-related childcare costs, health insurance premiums for the children, and extraordinary medical expenses not covered by insurance.

Education-related costs, such as private school or special education expenses, may also be included when appropriate. These added costs can significantly increase the total support obligation.

Step 5: Calculate each parent’s proportionate share

Each parent’s share of child support is based on their percentage of the combined income. If one parent earns 70% of the combined income, that parent is responsible for 70% of the total support obligation.

The parent with the higher obligation typically pays the difference to the other parent, rather than both parents exchanging payments.

Step 6: Adjust for parenting time

Parenting time plays an important role in Arizona child support calculations. The Arizona Child Support Guidelines apply parenting time adjustments on a sliding scale, with the adjustment increasing as a parent’s number of overnights increases.

This adjustment reflects the fact that a parent with more parenting time pays many direct child-related expenses during their time with the child. Shared or near-equal parenting time can significantly reduce the amount of child support owed, depending on each parent’s income and the overall allocation of expenses.

Factors affecting child support amounts

Even though Arizona uses a standardized formula, the final child support amount can vary widely. Several key factors influence how much support is ordered in your case.

Income disparity between parents

The difference between each parent’s income plays a major role. If one parent earns significantly more, that parent will be responsible for a larger share of the total support obligation. When incomes are closer and parenting time is shared evenly, support payments may be much lower or even offset.

Parenting time division

Parenting time directly affects child support in Arizona. The Arizona Child Support Guidelines apply parenting time adjustments on a sliding scale, with the adjustment increasing as a parent’s number of overnights increases. The more time you spend caring for your child, the more the formula accounts for the direct expenses you already cover during your parenting time.

Additional expenses

Child support is not limited to basic living costs. The court adds certain expenses to the base amount, including work-related childcare, health insurance premiums for the child, and extraordinary medical or dental costs. In some cases, private school tuition or special education expenses may also be included. These additions can significantly increase the total support obligation.

Multiple children from different relationships

If you already pay child support for other children, or you have different biological or adopted children living in your home, those obligations are factored into the calculation. Arizona adjusts available income to reflect existing responsibilities, which can reduce the amount owed in a new case.

Modifying child support orders

Child support orders are not permanent if circumstances change. Arizona allows modifications when there is a substantial and continuing change that affects the calculation.

Common reasons for modification include a significant increase or decrease in income, a change in parenting time, new or reduced childcare or health insurance costs, or changes in a child’s needs. In many cases, courts look for a change that would alter the support amount by at least 15%, or that occurs three years after the last order.

To request a modification, you must file a petition with updated financial information and formally serve the other parent. The court will review current income, expenses, and parenting time before deciding whether a change is justified.

When does child support end in Arizona?

In Arizona, child support does not automatically end on a child’s 18th birthday in every case. Support generally continues until the child turns 18 and graduates from high school. However, support cannot continue past the child’s 19th birthday.

This means that if a child turns 18 while still enrolled in high school, such as during their senior year, child support typically continues until graduation. Once the child graduates or turns 19, whichever happens first, the obligation ends unless the court has ordered otherwise.

Parents should be aware that support does not automatically terminate in all situations. In some cases, a formal request or confirmation may be required to stop wage withholding or enforcement actions. Reviewing the order and confirming the termination date can help prevent overpayment or enforcement issues.

Conclusion

Arizona does not use a simple percentage of income to calculate child support. Instead, the state applies the Income Shares Model, which considers both parents’ combined income, the number of children, parenting time, and additional expenses such as childcare and health insurance. Each parent’s obligation is based on their proportional share of the total child-rearing cost.

Understanding how Arizona calculates child support helps you better anticipate payments, identify errors, and know when a modification may be appropriate. Whether you are establishing support for the first time or reviewing an existing order, knowing how the formula works puts you in a stronger position to protect your financial stability and your child’s needs.