Idaho Tax Residency Rules 2026: The 270-Day Rule & 445-Day Exit

Who needs to read this

Idaho taxes residents on all income, wherever earned, at a flat 5.3%, and its residency statute has two features most states lack: a genuine bright-line day count (270) and a genuine statutory exit path (the 445-day rule). The details matter if:

• You split time between Idaho and a no-tax neighbor (Washington, Nevada, or Wyoming)
• You're leaving Idaho and want a defensible cut-over date
• You moved to Idaho (Boise's transplant wave) mid-year
• You're a remote worker living part of the year in an Idaho home
• You keep an Idaho cabin or second home while living elsewhere

How Idaho defines residency

Idaho Code §63-3013 makes you a resident if either:

1. You are "domiciled in the state of Idaho for the entire taxable year", or
2. You maintain a place of abode in Idaho for the entire taxable year and spend "in the aggregate more than two hundred seventy (270) days" of the year in Idaho.

Prong 2 is the statutory-resident trap for people domiciled elsewhere: keep a year-round Idaho home and spend more than 270 days in-state, and you're a resident no matter where your "real" home is. Note both halves must hold: the abode must be maintained for the entire year, and the days must exceed 270.

Prong 1 is where most disputes actually live. Domicile is your true, fixed, permanent home; if that's Idaho, you're a resident at any day count, subject to one statutory exception.

The 445-day absence rule. A domiciled Idahoan who leaves can be treated as a nonresident (part-year in the departure year) by being absent from Idaho at least 445 days in the first 15 months after leaving. The exception fails if your spouse or minor children occupy your permanent Idaho home more than 60 days in the year, if you claim Idaho as your federal tax home for deduction purposes, or if you hold certain federal offices. And it's fragile afterward: return for more than 60 days in any calendar year and you're an Idaho resident again.

Counting the days

Idaho's day tests count aggregate days of physical presence, so every stint in the state across the year adds up:

• The 270-day test is aggregate, not consecutive.
• The 445-day rule and its 60-day follow-on cap are counted the same way: days physically present in (or absent from) Idaho.
• The Tax Commission decides close cases on evidence, and the taxpayer supplies it. If you live near either line (270 days in, or 60 days back), a contemporaneous day-by-day location log is the difference between asserting your count and proving it.

Domicile: the stickier test

Idaho follows the classic rule: domicile is "the place where an individual has his true, fixed, permanent home and principal establishment, and to which place he has the intention of returning whenever he is absent." Once established, it persists until three things concur: intent to abandon the old domicile, intent to acquire a specific new one, and actual physical presence in the new one.

In practice the Tax Commission weighs the usual connections:

• Where your spouse and children live, and where the kids attend school
• Which home is the genuine base, and what happens to the Idaho house when you're gone
• Employment, business interests, and professional licenses
• Driver's license, voter registration, vehicle registration, and the address on your federal return
• Where your daily life (doctors, banking, community) actually happens

Working a season in another state, or wintering in Arizona, does not move your domicile. That's precisely why the 445-day rule exists: it lets a genuinely departed Idahoan stop being taxed as a resident before the slow work of re-domiciling is complete.

Part-year residents and nonresidents

Full-year residents file Form 40; part-year residents and nonresidents file Form 43:

• Full-year residents file Form 40 and pay Idaho tax on all income.
• Part-year residents file Form 43: Idaho taxes everything received while resident, plus Idaho-source income received while nonresident. The filing threshold is $2,500 of combined gross income.
• Nonresidents file Form 43 if Idaho-source gross income exceeds $2,500. Idaho-source income includes wages for work physically performed in Idaho, Idaho rental income, and income from an Idaho business or partnership.

Idaho's rate is a flat 5.3% (House Bill 40, signed March 2025, retroactive to January 1, 2025), after a zero-rate band: for 2025, no tax on roughly the first $4,800 of taxable income for single filers, $9,600 for joint filers.

Changing your residency status

Leaving Idaho cleanly means winning on one of two tracks:

• Change domicile for real: establish the new home, move the family, shift licenses, registrations, banking, and daily life, and be physically present in the new state with intent to stay
• Or ride the 445-day rule: leave, stay out 445 of the first 15 months, keep future Idaho visits under 60 days a year, keep family out of the old house for more than 60 days a year, and don't claim Idaho as your federal tax home
• Either way, document the dates: departure, arrival, and every Idaho day afterward
• Moving to Idaho: your resident period starts when domicile shifts or when the abode-plus-days pattern begins; file Form 43 for the split year with a consistent date

How Idaho enforces its rules

The Tax Commission runs a steady, decision-generating residency program: its published rulings regularly involve departed residents who kept the house, the spouse, or the tax home.

• The house is the anchor. A maintained year-round abode is one of the two statutory elements, and family occupying it can void the 445-day exception outright.
• Federal filings are checked: claiming Idaho as your tax home for federal travel deductions while filing as a nonresident is a listed disqualifier.
• Licenses, registrations, and filing-history changes (Form 40 one year, absent the next) are routine flags.
• The stakes: reclassification to resident means the flat 5.3% on all income for the years at issue, plus interest and penalties.

Common mistakes

• Reading 270 as the whole rule. It only shields people domiciled elsewhere. Idaho domiciliaries are residents at any day count unless they satisfy the 445-day exception.
• Botching the 445-day math. It's 445 days of absence within the first 15 months; a couple of long trips home can quietly break it.
• Leaving the family in the house. Spouse or minor children occupying your Idaho home more than 60 days a year kills the absence exception.
• Keeping Idaho as your federal tax home. Deducting travel "away from home" in Boise while claiming nonresidency contradicts yourself in writing.
• Coming back too much. After a successful exit under the 445-day rule, more than 60 Idaho days in any calendar year makes you a resident again.
• No day records. Both statutory tests are pure day-count questions; without a log, the aggregate is whatever the evidence says it is.