Article 23(2) of the 2008 Bhutan Constitution discusses the right to vote: "A person shall have the right to vote by direct adult suffrage through secret ballot at an election if the person is: (a) A Bhutanese citizen as evidenced by a Citizenship Card: (b) Not less than eighteen years of age: (c) Registered in the civil registry of that constituency for not less than one year, prior to the date of the election; and (d) Not otherwise disqualified from voting under any law in force in Bhutan.

References:

2008 Constitution of the Kingdom of Bhutan: "Article 23: Elections," Constitution of the Kingdom of Bhutan, 2008 : 46-47: https://heinonline-org.proxygw.wrlc.org/HOL/Page collection=cow&handle=hein.cow/zzbt0002&id=55&men_tab=srchresults