How is child support calculated in Michigan?

Michigan has Child Support Guidelines which consider both parent's incomes, the number of children involved, and various custodial arrangements, such as "primary custody" and "joint/shared custody."

Until October 2008, there were 3 tiers for custody.  Support was based upon "primary custody" if one parent had the children the majority of the time while the other parent enjoyed a given amount of parenting time. "Joint/shared custody" meant 50-50 if each parent had the children for 182.5 overnights. If time spent was not "50-50" then the next tier kicked in, which was called "shared economic responsibility" and was based on the assumption that one parent had 237 overnights and the other, 128 overnights per year.

Obviously, this was an artifical distinction and many parents paid too much because, even if they enjoyed 100 overnights with their children, it still fell below 50-50 requirement and so dropped down to the "shared economic responsibility" level.  Since October 2008, the Michigan Child Support Formula began calculating support based upon the actual number of overnights.  Support can be reviewed at a parent's request every 36 months, or any time there is a change in circumstances (such as a change in the number of overnights).