Wash. Rev. Code § 59.18 § 59.18.700

(1)(a) Except as authorized by an exemption under RCW 59.18.710 , a landlord may not increase the rent for any type of tenancy, regardless of whether the tenancy is month-to-month or for a term greater or lesser than month-to-month:
(i) During the first 12 months after the tenancy begins; and
(ii) During any 12-month period of the tenancy, in an amount greater than seven percent plus the consumer price index, or 10 percent, whichever is less.
(b) This subsection (1) does not prohibit a landlord from adjusting the rent by any amount after a tenant vacates the dwelling unit and the tenancy ends.
(c) Beginning June 1, 2025, and annually thereafter, the department of commerce shall calculate the maximum annual rent increase percentage allowed under (a) of this subsection for the following calendar year and publish the information on their website and in a press release. For the purposes of this subsection, "consumer price index" means the June 12-month percent change in the consumer price index for all urban consumers, all items, for the Seattle area as published by the United States bureau of labor statistics.
(2) If a landlord increases the rent above the amount allowed in subsection (1) of this section as authorized by an exemption under RCW 59.18.710 , the landlord must include facts supporting any claimed exemptions in the written notice of the rent increase. Notice must comply with this section, RCW 59.18.720 , 59.18.140 , and be served in accordance with RCW 59.12.040 .
(3) If a landlord increases rent above the amount allowed in subsection (1) of this section and the increase is not authorized by an exemption under RCW 59.18.710 , the tenant must offer the landlord an opportunity to cure the unauthorized increase by providing the landlord with a written demand to reduce the increase to an amount that complies with the limit created in this section. In addition to any other remedies or relief available under this chapter or other law, the tenant may terminate the rental agreement at any time prior to the effective date of the increase by providing the landlord with written notice at least 20 days before terminating the rental agreement. If a tenant terminates a rental agreement under this subsection, the tenant owes rent for the full month in which the tenant vacates the dwelling unit. A landlord may not charge a tenant any fines or fees for terminating a rental agreement under this subsection.
(4)(a) Except as provided in (b) of this subsection, a landlord may not include terms of payment or other material conditions in a rental agreement that are more burdensome to a tenant for a month-to-month rental agreement than for a rental agreement where the term is greater or lesser than month-to-month, or vice versa.
(b) A landlord must provide parity between lease types with respect to the amount of rent charged for a specific dwelling unit. For the purposes of this subsection, "parity between lease types" means that, for leases or rental agreements that a landlord offers for a specific dwelling unit, the landlord may not charge a tenant more than a five percent difference in rent depending on the type of lease or rental agreement offered, regardless of whether the type of lease or rental agreement offered is on a month-to-month or other periodic basis or for a specified period. This five percent difference may not cause the rent charged for a specific dwelling unit to exceed the rent increase limit in subsection (1) of this section.
(5)(a) A tenant or the attorney general may bring an action in a court of competent jurisdiction to enforce compliance with this section or RCW 59.18.710 , 59.18.720 , or 59.18.140 . If the court finds that a landlord violated any of the laws listed in this subsection, the court shall award the following damages to the tenant and attorneys' fees and costs to the tenant who brings the action or the attorney general:
(i) Damages in the amount of any excess rent, fees, or other costs paid by the tenant;
(ii) Damages in an amount of up to three months of any unlawful rent, fees, or other costs charged by the landlord; and
(iii) Reasonable attorneys' fees and costs incurred in bringing the action.
(b) The attorney general may bring an action under this subsection notwithstanding whether the tenant has offered the landlord an opportunity to cure, and may recover civil penalties of not more than $7,500 for each violation in addition to other remedies provided by this subsection. The attorney general may issue written civil investigative demands for pertinent documents, answers to written interrogatories, or oral testimony as required to investigate or bring an action under this subsection.
(6) The remedies provided by this section are in addition to any other remedies provided by law.
(7) A landlord may not report the tenant to a tenant screening service provider for failure to pay the portion of the tenant's rent that was unlawfully increased in violation of this section.
(8) This section expires July 1, 2040.