The parent who does not have primary physical residence of the child will generally have to pay, however, the amount of support that will be paid may be less if the child spends at least 40% of his or her time with an access parent.
Since the child is spending almost equal amounts of time with both parents then the expenses that they may have, that are associated with taking care of the child, will be more or less the same and as a result they should not have to pay an excessive amount of support which could then result in a windfall gain to one parent and undue hardship to the other.
It seems as though, however, the courts are most concerned with the standard of living of the child involved and will probably try to award an amount that will allow the parents to maintain that standard of living.
Establishing the 40% threshold requirement may be difficult as courts have been inconsistent with the factors used in order to make this determination. Some judges include weekends, holidays and overnight stays (i.e. the hours during which the child is sleeping) in the calculation of the 40% whereas others do not. Unfortunately, there is no bright-line rule dictating what is required in order to meet the threshold.