How long does it take to complete the tax questionnaire? Support Resources August 10, 2016 00:20 Updated Follow If you have all of the information needed, the questionnaire should take 30-45 minutes to complete. To find out what documents you need on hand for each form, check out this FAQ. Related articles When do I have to complete my tax questionnaire? Can you use the tax questionnaire I completed last year? Comments 0 comments Article is closed for comments.