Monthly insurance premiums related to insured persons must be paid by the last day of the following month; provided however, that insurance premiums relating to insured persons with optional and continued coverage must be made by the 10th day of the following (a day specified by the insurer for the first payment of an insurance premium).
When an insurer (meaning JHIA if the relevant insured person has optional and continued coverage under the health insurance program administered by JHIA; a health insurance society if the relevant insured person is covered by a health insurance program administered by a health insurance society; or otherwise, the Minister of Health, Labour and Welfare; the same applies in the following paragraph) finds that the notified amount of insurance premium exceeds the amount to be paid for the insurance premium after the notice of insurance premium payment concerning an insured person is given, or that an insured person has paid an amount of insurance premium that exceeds the amount to be paid for the insurance premium, the notice of payment or the payment of the excessive amount may be deemed as prepayment for the insurance premium to be paid before the due date within six months after the day of the notice or payment.
保険者等（被保険者が協会が管掌する健康保険の任意継続被保険者である場合は協会、被保険者が健康保険組合が管掌する健康保険の被保険者である場合は当該健康保険組合、これら以外の場合は厚生労働大臣をいう。次項において同じ。）は、被保険者に関する保険料の納入の告知をした後に告知をした保険料額が当該納付義務者の納付すべき保険料額を超えていることを知ったとき、又は納付した被保険者に関する保険料額が当該納付義務者の納付すべき保険料額を超えていることを知ったときは、その超えている部分に関する納入の告知又は納付を、その告知又は納付の日の翌日から六月以内の期日に納付されるべき保険料について納期を繰り上げてしたものとみなすことができる。