Age of Majority
The age of majority in Washington is age 18. If you're filing for divorce and you have a child who is 18 or older, your decree may or may not include a child support obligation, depending on several circumstances and whether you have other children. Even if you are not legally obligated to pay child support for your 18-year-old, you would still have to pay for your younger children. However, your obligation would be reduced somewhat because it provides for one less dependent.
Other Factors for Support
If your child turns 18 in January but doesn't graduate from high school until June, your decree will probably include provisions that you pay support until she finishes school. If it's silent on the issue, giving no specific cutoff date, your support obligation terminates on her 18th birthday. Your spouse can file a motion with the court at that time, asking to continue the support order until your child graduates. If your child is disabled and incapable of caring for herself, support can continue indefinitely or until she's no longer considered disabled. Other factors can terminate support sooner than your child's 18th birthday. For example, if she marries before turning 18, she moves beyond her need for your support and your obligation ends.
If your child wants to go to college, your financial obligation may be extended. Depending on how old she is when your divorce is final, provisions for post-secondary education might be included in your decree, or you might have to go back to court later to address them. Washington State courts are willing to order support for college expenses if your child enrolls at an accredited institution. The judge weighs several factors when deciding whether to make you responsible for at least some of these educational costs. These factors would likely include whether your child always intended to go college, if she would have gone to college if you and your spouse had stayed married -- and if so, how much financial help you would have provided for her. If the court orders support for college past the age of 18, you may be able to pay your child directly, or make payments to her school. In no case would this support continue past her 23rd birthday.
According to Washington attorney Molly B. Kenny, you can legally stop paying support when your child achieves an event that terminates it by law, such as reaching 18 or getting married. If you have other, younger children, however, you have to file a motion with the court for modification of the support terms of your decree. If your divorce isn't final yet, you can make a request of the court to have a specific time of termination included in your decree, such as age 18, or upon completion of high school. This can avoid confusion later on.