In Washington State, income may be imputed to a parent for purposes of calculating child support if the parent is voluntarily unemployed or underemployed (i.e. does not have actual full time income).
The reason behind this, as I understand it, is the idea that a parent should not be able to avoid child support responsibilities by choosing not to work. This means that the courts can set child support based on what it appears the parent would be making if employed full time.
In determining what the imputed income should be, the court can look at a number of factors, including the person’s current rate of pay at part time work (just multiply that hourly rate out to full time), their rate of pay at the last job they did work, or using a table of average incomes based on age and gender.
A key here is that the unemployment or underemployment must be “voluntary”. That means the person could be working more but is choosing not to. Income should not be imputed if the person is able to show that they are not able to work.
Sometimes the question comes up whether it is “underemployment” if a person is working full time but could be making more in another job. My experience has been that the courts do not find a person underemployed if they have full time work, but I have heard rumors at least of decisions going the other way.