N.D. Cent. Code § 40-45-08
Every member of the police department shall pay to the treasurer of the pension fund a membership fee to be fixed by the board of trustees in an amount not exceeding twenty-five dollars. Each member shall be assessed and required to pay annually an amount not less than three percent or more than five percent per annum as determined by the governing body of the municipality upon the amount of the annual salary paid to the member. Such assessment shall be deducted and retained in equal monthly installments out of such salary. Assessments shall be made of all members for a minimum period of fifteen years for partial retirement and for twenty years and for such additional years as may be determined by the governing body for full retirement, as provided by section 40-45-09.
N.D.C.C. § 40-45-08