How Child Support Is Calculated in Michigan

Child support is one of the few parts of a Michigan family case with a formula. That does not make it simple. The Michigan Child Support Formula (MCSF), published by the State Court Administrative Office's Friend of the Court Bureau, runs to dozens of pages, and the inputs often matter more than the math. Under MCL 552.605, a court must order the amount the formula produces unless it finds that result unjust or inappropriate and explains, on the record, how and why it is deviating.

Here is how the calculation actually works, step by step. If you want to try your own numbers as you read, our free Michigan child support calculator uses the current 2025 formula.

Step 1: Each Parent's Net Income

Everything starts with income. The formula counts nearly every source: wages, overtime, commissions, bonuses, self-employment and business income, rental income, unemployment, disability and more. From that gross figure it subtracts income taxes, Social Security and Medicare, and certain mandatory deductions to arrive at net income.

Three income issues come up constantly:

• Self-employment and business owners. Business owners control what shows up as income. Depreciation, personal expenses run through the business and retained earnings are frequently disputed.
• Imputed income. If a parent is voluntarily unemployed or underemployed, the court can calculate support based on the income that parent could earn, considering education, work history, health and the local job market.
• Other children. A parent who supports children from another relationship gets an adjustment that reduces the income used in the calculation.

Step 2: The Base Support Amount From the Tables

Next, the formula adds the parents' net incomes together and applies the General Care Support tables for the number of children. The tables reflect what families at that combined income level typically spend on children. The percentage goes down as income goes up, so a family earning twice as much does not pay twice as much support.

That family amount is then divided by each parent's share of the combined net income. If one parent earns two thirds of the combined income, that parent's base obligation is two thirds of the table amount.

For lower-income parents, the formula has protections. A parent whose income is below the Low Income Threshold ($1,255 per month in the 2025 formula) pays a minimal amount, and a transition calculation keeps support from consuming too much of a low earner's income.

Step 3: The Parental Time Offset

This is where overnights come in, and it is often the most contested part of the calculation. Each parent's base obligation is run through the parental time offset, an equation that uses the number of overnights each parent has per year. The more overnights the paying parent has, the lower the support.

The offset is not a straight line. Because the equation uses each parent's overnights raised to the power of 2.5, the effect grows quickly as the schedule approaches equal time. Moving from 80 to 120 overnights reduces support far less than moving from 140 to 180. That is why a few overnights near the middle of the range can make a real financial difference, and why the parenting time schedule and child support should be negotiated together, not separately.

Equal parenting time does not mean zero support. If one parent earns significantly more, that parent usually still pays, just less.

Step 4: Health Care

The formula then addresses three kinds of health care costs:

• Insurance premiums. The portion of a parent's health insurance premium that covers the children is shared between the parents by income percentage.
• Ordinary medical expenses. The paying parent contributes a share of a fixed annual amount per child, built into the monthly support, for routine costs such as co-pays and over-the-counter items.
• Extraordinary expenses. Uninsured costs above the ordinary amount, such as orthodontics, therapy or a major medical bill, are typically divided by income percentage as they occur.

Step 5: Child Care

Work-related child care costs are divided between the parents according to their income shares. A parent who pays for daycare or after-school care while working can recover the other parent's share through the support order. Child care often changes as children get older, which makes it a common reason to revisit support later.

A Worked Example

Consider two parents with one child. Parent A has net income of $3,000 per month. Parent B has net income of $6,000 per month. The child spends 261 overnights a year with Parent A and 104 with Parent B. No one pays for child care or insurance in this example.

1. Combined net income is $9,000. The 2025 support table produces a family amount of about $1,666 per month for one child.
2. Parent B earns 66.67% of the combined income, so Parent B's base share is about $1,110. Parent A's share is about $555.
3. Applying the parental time offset with 104 overnights for Parent B reduces Parent B's obligation to about $958.
4. Adding Parent B's share of ordinary medical expenses brings the total to roughly $969 per month.

If the same parents had a schedule close to equal time (183 and 182 overnights), Parent B's base support would drop to about $283 per month, because Parent B still earns twice as much. If Parent B had no overnights at all, it would be about $1,110 plus ordinary medical.

These numbers come from the same engine as our calculator. Real cases add taxes on actual gross income, insurance, child care and other adjustments, so treat this as an illustration, not a prediction.

When the Court Can Depart From the Formula

Under MCL 552.605, a judge may deviate from the formula when applying it would be unjust or inappropriate. The court must state the formula amount, how the order deviates, the value of any property or other support awarded instead, and the reasons. Parents can agree to a deviation, but the same requirements apply, and the judge must still approve it. Very high incomes, a child with special needs, or a property settlement that substitutes for support are common reasons to look at deviation.

How Long Support Lasts and When It Changes

Child support generally continues until the child turns 18. Under MCL 552.605b, the court can extend support while the child is regularly attending high school full time with a reasonable expectation of graduating and living with the parent receiving support, but never past 19 and a half. Michigan courts cannot order college support unless the parents agree to it.

Support can be reviewed and modified when circumstances change. Timing matters: under MCL 552.603, support cannot be changed retroactively before the date the other parent received notice of the request. For more, see How to Modify Child Support in Michigan.

Why the Inputs Matter More Than the Math

Once the inputs are set, the Friend of the Court's software does the arithmetic. The outcome is decided by the inputs: what counts as income, whether income should be imputed, the real overnight count, who pays for insurance and child care, and whether a deviation is justified. Those are the questions where careful preparation and advocacy change the number.

If you are facing a child support calculation in a divorce, custody case or modification, a free, confidential consultation can help you understand where your number is likely to land and what can move it.