When Children Live in Two Homes: What Tannehill v. Tannehill Tells Us About Split-Custody Support in Maryland

Maryland's child support system is built around a structured formula, but that formula wasn’t designed to handle every family situation neatly. When children from the same marriage are divided between two households, the legal term is "split custody," and calculating support in such cases requires analysis that goes well beyond the standard guidelines worksheet.

One case has shaped how Maryland courts approach this calculation for more than three decades: Tannehill v. Tannehill, 88 Md. App. 4 (1991). It remains a foundational reference point for courts, attorneys, and families navigating custody and support arrangements in Maryland.

If you're facing a split-custody situation and have questions about how child support is determined, Law Offices of Thomas Stahl is ready to help. Call (443) 300-9208 or contact our office to schedule a consultation.

What Split-Custody Means Under Maryland Law

Before understanding how support is calculated, it's worth clarifying what split custody means. Split custody is not the same as shared physical custody. In a shared custody arrangement, both parents have primary physical custody of the same children, with each parent having the children for a meaningful portion of the year. Maryland currently defines shared physical custody as each parent having the children for at least 25% of the time.

Split custody is a different situation entirely. It occurs when parents have more than one child together, and at least one child lives primarily with each parent. For example, if there are three children and one parent has primary custody of two while the other parent has primary custody of one, that arrangement qualifies as split custody. The children are split between the households, not the parenting time for a single child.

This distinction matters because split custody requires the court to calculate what each parent effectively owes the other and then determine the net payment.

What Tannehill v. Tannehill Established

The Tannehill case arose from a divorce in Charles County, Maryland, in which four children were ultimately divided between both parents. Three children remained with the father, and one child with significant medical needs was placed in the mother's care. The trial court's calculation of child support was challenged on appeal, and the Maryland Court of Special Appeals used the case to lay out a logical framework for applying the Maryland Child Support Guidelines to split-custody cases.

The real doctrinal contribution of Tannehill was that courts must apply the Maryland Child Support Guidelines, treat the guideline amount as presumptively correct, and, if deviating from that amount, state the guideline calculation on the record and explain why the deviation is justified. While the case discussed the mechanics of calculating support in split-custody situations, it is most frequently cited for the broader principle that guideline calculations are mandatory and deviations must be clearly justified.

In clarifying the application of the Maryland Child Support Guidelines, the court described the framework that trial courts should follow when calculating support in split-custody cases:

First, the court calculates the basic child support obligation under the Maryland Child Support Guidelines using the parents’ combined adjusted income, and then applies the calculation separately for the children in each parent’s primary custody.
Second, each parent's proportionate share of that combined income is calculated as a percentage. That percentage is then applied to determine how much each parent owes the other.
Third, rather than requiring both parents to exchange support payments, the parent with the higher obligation pays the difference, a net payment that accounts for what both parents effectively owe.

The court's framework was designed to reflect the reality that both parents are supporting children simultaneously and that fairness requires accounting for that burden on both sides.

Why Similar Cases Can Produce Very Different Outcomes

One of the most important things families must understand about split-custody support calculations is that even when the legal framework is the same, the results can vary significantly from case to case. This is not a flaw in the system. It reflects the reality that the calculation depends entirely on the specific facts before the court.

The following factors can push outcomes in different directions:

Income disparity between parents – The percentage-based income-sharing model means that a wide gap in earnings will significantly affect what each parent owes. A parent earning 70% of the household's combined income will bear a larger share of the support obligation regardless of which parent has more children.
The number of children in each parent's custody – Because the basic support obligation must be calculated under the guidelines for the children residing in each parent’s household, a parent with two children in their primary care is in a different position than a parent with one. The support schedules are graduated, and having more children in your custody does not automatically reduce your net payment.
Extraordinary expenses – Medical costs, childcare, and other qualifying expenses are added to the basic obligation and divided between parents proportionally. A child with significant medical needs, as was the situation in Tannehill itself, can substantially alter the final numbers. How the court treats those expenses, whether they offset support, whether insurance coverage changes the calculation, is a fact-specific analysis.
Judicial discretion to deviate from the guidelines – Maryland law presumes the guideline amount is correct, but courts may depart from it when applying the formula would yield an unjust or inappropriate result. When a court deviates, it must explain its reasoning on the record, including how the deviation serves the children's best interests. Tannehill and subsequent cases reinforce that the guideline amount is the presumptively correct starting point, but courts retain limited discretion to deviate when applying the formula would produce an unjust or inappropriate result, provided the court explains the deviation on the record.
Changes in circumstances – A split-custody support order entered years ago may no longer reflect current incomes, custody arrangements, or children's needs. As children age out of the arrangement, as incomes change, or as one child's primary residence shifts, the calculation can change substantially.

The Larger Picture: Why Consistency Is Difficult to Guarantee

The fact that the Tannehill framework can produce different outcomes across cases does not mean the courts are being arbitrary. It means that the law requires individualized analysis. Two families with split-custody arrangements and similar incomes can receive different support outcomes because the details of their situations differ in ways that matter legally.

This is why guidance from an attorney who understands how Maryland courts apply these guidelines in practice can be so important. The formula provides the structure for calculating support, but reaching a fair outcome often depends on how the facts are presented, which expenses are properly included, and whether any circumstances justify a departure from the standard calculation.

Protecting Your Children's Interests When Custody Is Divided

For Maryland families dealing with split custody, what matters most is not the formula itself but whether the final support arrangement reflects the true cost of raising children across two households. Courts are focused on the best interests of the children, and support calculations are one tool for serving that interest.

When custody divides children between parents, the legal and financial questions become more complex quickly. Getting those calculations right and building an order that can be modified if circumstances change is essential for the stability of both families.

Law Offices of Thomas Stahl works with families in Columbia and the surrounding areas on child custody and support matters.

Call (443) 300-9208 or reach out online to speak with an attorney about how Maryland's child support guidelines apply to your situation.