It's really hard to tell you what would be average because child support is based on incomes. So average for one family is insanely high or ridiculously low for another. Below is a link to the WA Child Support Calculator. Also I have linked the WA Child Support Schedule which has all of the amounts for all incomes. If this is the only kid he supports, then you look at the "One Child Family." If the child is less than 12 years old, you use the amounts from Column A of One Child Family. The child support schedule itself is within a long set of instructions for filling out a child support worksheet. Scroll through the link to page 11 (or 16) and the schedule is right there.