would a greater-time parent with an extremely high income be ordered to pay child support to the parent
who has the child for less than 30 percent time. In contrast, a state with a 20 percent threshold could allow
for an order of child support from the greater-time parent to the lesser-time parent with a time-share level
as low as 21 percent (given a very high income of the greater-time parent).
In the following discussion we divide offset formulas into three groups based on their relationship
to the definition of threshold. The first set has no threshold, and we refer to this as a “without threshold
offset formula.” This type of offset formula is currently used only in the state of California. California’s
guidelines apply to all child support cases, sole and shared custody alike, without a threshold to
The second group we refer to as “below-threshold offset” formulas. The mathematics of these
formulas are based on a reduction calculation which begins at one day, or 1 percent, well below any
defined threshold, and a state’s threshold is not embedded in the formula. The child support reduction
calculated by these formulas is not applied until a case has passed the threshold. Each state uniquely
defines its threshold, but the formula is identical in all states that use one of the below-threshold offset
variations. This is the most common shared custody formula in use today. It has several variations, which
we will consider.
The third type of offset formula we characterize as an “above-threshold offset” formula. The
threshold, as defined by each state, is embedded in the mathematics of the formula itself. We consider this
approach to be the most equitable approach to child support calculation in shared custody cases in use
today, for reasons we discuss below.
Without Threshold Offset Formula. This formula, as employed in the state of California, is based
on a rather complex formulation that is a function of father’s income, mother’s income, father’s time with