Idaho Tax Residency (270-day rule)

Key parameters
Threshold	270 days
Period / Window	Tax year (1 Jan – 31 Dec)
Counting	Any part of a day
Alternative	Domicile
Additional requirements	Abode kept the entire year

This applies to anyone keeping a home in Idaho year-round, whichever state they treat as their own. You are an Idaho resident if either of these applies:

• Domicile for the entire tax year — Idaho is your permanent home for all twelve months, not merely part of them.
• Abode plus days — you maintain a place of abode in Idaho for the entire tax year and spend more than 270 days of that year in the state.

More than 270 days is roughly nine months, the highest day threshold any state applies.

The abode condition is correspondingly strict. It must be maintained for the entire tax year rather than for substantially all of it or for six months, so acquiring or giving up an Idaho home partway through the year defeats the test regardless of how the day count falls.

• The abode must cover all twelve months. Unlike states asking for substantially all of the year, Idaho requires the entire tax year, so a mid-year purchase or sale defeats the limb.
• Individual days can be excluded. Presence for a temporary or transitory purpose on a given day does not count, which is a per-day exception rather than a whole-stay one.
• 270 days is a high bar. Someone can spend two-thirds of the year in Idaho and still fall outside the statutory route entirely.
• Domicile must also cover the full year. Being domiciled in Idaho for only part of the year puts you outside that route, though a part-year filing may still be required.
• Falling outside both routes is not the end of it. Idaho-source income remains taxable whatever your residency status.

A resident is taxed on income from all sources while a nonresident pays only on Idaho-source income, so an error usually surfaces as out-of-state earnings never reported while another state taxed the same income. The Tax Commission charges interest from the original due date and adds penalties for filing late and for underpaying, with higher exposure where an understatement is treated as deliberate. Professional tax advice is strongly recommended in situations like this.

A year-round home and a long stay

You are domiciled in Nevada, own a house in Boise available to you all year, and spend about 290 days in Idaho. Both limbs hold, so you are an Idaho resident for the year.

A high count without a full-year home

You spend 300 days in Idaho but only buy your house there in March. The abode was not maintained for the entire tax year, so the statutory route fails despite an ample day count.

A full-year home and a shorter stay

You keep an Idaho cabin available all year and spend around 250 days in the state. The abode limb holds but the count falls short of 270, so the rule does not attach.

• Idaho State Tax Commission — Individual income tax
• Idaho State Tax Commission — Residency audit manual