ORS § 743.471
A health insurance policy may contain a provision as follows: "CANCELLATION: The insurer may cancel this policy by written notice delivered to the insured, or mailed to the last address of the insured as shown by the records of the insurer. The notice must state the reason for cancellation and the date on which the cancellation shall be effective. Except as provided under the 'GRACE PERIOD' provision of this policy for nonpayment of premium, cancellation shall not become effective earlier than the 30th day after the date of the notice. After the policy has been continued beyond its original term, the insured may cancel this policy at any time by written notice delivered or mailed to the insurer, effective upon receipt or on such later date as may be specified in such notice. In the event of cancellation, the insurer will return promptly the unearned portion of any premium paid. If the insured cancels, the earned premium shall be computed by the use of the short rate table last filed with the state official having supervision of insurance in the state where the insured resided when the policy was issued. If the insurer cancels, the earned premium shall be computed pro rata. Cancellation shall be without prejudice to any claim originating prior to the effective date of cancellation."
ORS 743.471