Taxpayers must file a Idaho state income tax return if the taxpayer was a full-year resident of Idaho for that tax year. Taxpayers who domiciled in the state with a bona fide intent to make permanent residency for 6 months or who spent more than 270 days or above are also required to file. If the taxpayer lived outside of the state but consider Idaho as their permanent home are also defined as a resident of Idaho. Form 40 is the Idaho state income tax return form for all full-time residents. Due date falls on April 15th of that tax year. If the due date falls on a Saturday, Sunday, or federal holiday, the due date is moved to the next business day.