Unless the judgment provides that there is no interest on the judgment amount, the judgment debtor will need to pay interest. For the last few years, the default interest rate for judgments in WA has been 12%, simple, computed annually.
Some credit card companies charge 50% annual compound interest. The companies get away with this high rate because they are not regulated by WA.
The judgment should have an interest rate indicated on it. You should contact the court to obtain a copy of the judgment.