# How to Calculate Custody Percentage

By Beverly Bird

Some state courts calculate parenting time based on the number of overnights your child spends with you each year. Others calculate it by hours. Either way, it affects the amount of child support the court orders you to pay at the time of your divorce, as well as later child support modifications.

## Calculating Child Support

When parents divorce, most states calculate child support based on a formula called the income shares model. The formula sets aside a portion of both parents’ combined incomes for their children’s financial needs, such as food and shelter. Both parents are responsible for paying a percentage of that portion, based on the percentage they contribute to their combined income total. For example, if Dad earns 65 percent of the parents’ combined incomes, and if he is the non-custodial parent, he would pay child support equal to 65 percent of the portion the court allots to the children. The custodial parent contributes her percentage by paying the child’s expenses directly. But this is a base number, and it assumes that his child never spends any time with the non-custodial parent. Courts make further calculations after arriving at this figure.

## Importance of Custody Percentage

When parents divorce, courts determine a parenting plan first, then calculate child support, because support is based on the projected amount of time a child will spend with each parent per year. The law acknowledges that when a non-custodial parent has his child with him, he is paying direct expenses on her behalf during those times. Therefore, the more time his child spends with him, the more it whittles away at the base child support amount. This saves him from paying twice -- once to the custodial parent through child support, and again for direct costs when his child is living with him.