Wash. Rev. Code § 63.14.158
The holder of a retail installment contract or contracts may, upon agreement in writing with the buyer, refinance the payment of the unpaid time balance or balances of the contract or contracts by providing for a new schedule of installment payments.
The holder may charge and contract for the payment of a refinance charge by the buyer and collect and receive the same but such refinance charge (1) shall be based upon the amount refinanced, plus any additional cost of insurance and of official fees incident to such refinancing, after the deduction of a refund credit in an amount equal to that to which the buyer would have been entitled under RCW 63.14.080 if he or she had prepaid in full his or her obligations under the contract or contracts, but in computing such refund credit there shall not be allowed the minimum earned service charge as authorized by subsection (1)(d) of such section, and (2) may not exceed the rate of service charge provided under RCW 63.14.130. Such agreement for refinancing may also provide for the payment by the buyer of the additional cost to the holder of the contract or contracts of premiums for continuing in force, until the maturity of the contract or contracts as refinanced, any insurance coverages provided for therein, subject to the provisions of RCW 63.14.140.
The refinancing agreement shall set forth the amount of the unpaid time balance or balances to be refinanced, the amount of any refund credit, the amount to be refinanced after the deduction of the refund credit, the amount or rate of the service charge under the refinancing agreement, any additional cost of insurance and of official fees to the buyer, the new unpaid time balance, if the service charge is stated as a dollar amount, and the new schedule of installment payments. Where there is a consolidation of two or more contracts, then the provisions of RCW 63.14.110 shall apply.
RCW 63.14.158
Minimum earned service charges: RCW 63.14.080.