N.D. Cent. Code § 13-01.1-02: When interest payment required

Interest must accrue and be made on payments overdue under section 13-01.1-01 at the rate of one and three-fourths percent per month, unless a different rate is specified within the contract upon which the claim is based. Interest must accrue beginning on the day after payment is due, if payment due date is specified by contract, or on the day of receipt of the invoice covering the delivered goods or services, if payment is not made within forty-five days. Interest ceases to accrue on the date payment is made.