Idaho Capital Gains Tax, Explained

Idaho has spent the past several legislative sessions cutting its income tax rate, and capital gains ride along for the whole trip because the state doesn't tax gains any differently than wages or business income. The current rate is a flat 5.3%, cut from 5.695% by House Bill 40, which Governor Little signed on March 6, 2025, effective retroactively to January 1, 2025. That rate carries into 2026 with no further scheduled cut currently in effect.

The move to a single flat rate is itself relatively recent. Idaho ran a multi-bracket system with a top rate above 6% as recently as a few years ago, and collapsed to one flat rate through a series of cuts before HB 40 trimmed it further. The direction has been consistently downward, and every gain you realize, on stock, a rental, or a business you built in Boise or Coeur d'Alene, gets the benefit of whatever the current flat rate is.

Notice the first row: a long-term gain the IRS taxes at 0% is still Idaho income at 5.3%. That table assumes no qualifying deduction. If your asset qualifies for the deduction described next, the Idaho column drops sharply.

Most states with a flat income tax apply that one rate to every gain with no exceptions. Idaho is the exception to that pattern, and it's an angle most sellers never hear about from a national tax blog. Idaho Code 63-3022H lets you deduct up to 60% of the capital gain net income from the sale of qualifying Idaho property, before the 5.3% rate ever touches it.

Two categories qualify. First, real property located in Idaho and held for at least 12 months, land, buildings, easements, grazing permits. Second, tangible personal property used in a revenue-producing enterprise (agriculture, manufacturing, wholesale distribution, feedlots, qualifying research operations), also located in Idaho and held at least 12 months, with a longer 24-month hold for cattle, horses, and timber. The deduction is claimed on Form CG.

What doesn't qualify matters just as much: stocks, bonds, crypto, partnership interests, and any intangible property are excluded entirely, no matter how long you hold them. Property located outside Idaho doesn't qualify either, even if you're an Idaho resident when you sell it.

Worked example: you sell Idaho farmland you've owned for six years, for a $200,000 gain, and it qualifies under Form CG. Without the deduction, Idaho tax would be $200,000 x 5.3% = $10,600. With the 60% deduction, only $80,000 of the gain is taxable to Idaho: $80,000 x 5.3% = $4,240, a savings of $6,360 on the state return alone.

The federal system sorts your gains into buckets: short-term at ordinary rates, long-term at 0%, 15%, or 20%, with the 3.8% NIIT layered on above $200K/$250K MAGI. Idaho starts from your federal taxable income and applies its flat rate, minus the Form CG deduction where it applies. That structural feature means most federal planning moves do double duty with no separate state election to file.

• Loss harvesting: losses that offset gains federally shrink the Idaho number in the same motion.
• Gain timing: a gain pushed into a lower federal bracket year saves at both layers at once.
• 1031 exchanges: gain deferred federally generally stays out of Idaho income too.
• Installment sales: spreading a gain across years spreads the Idaho bill along with the federal one.

On the federal side, a rental sale splits into layers: the depreciation you claimed comes back as recapture at up to 25%, the remaining gain gets long-term rates, and the NIIT can ride on top. Idaho doesn't carve out a separate recapture rate. It applies the flat 5.3% to the taxable Idaho gain, after the Form CG deduction if the property qualifies.

Worked example: you sell a Boise-area rental you've held for four years for a $200,000 total gain, of which $60,000 is depreciation recapture, and you're in the 15% federal bracket. Federal: $60,000 x 25% = $15,000, plus $140,000 x 15% = $21,000, for $36,000. If the property qualifies for the Idaho deduction (Idaho real property, held over 12 months), only 40% of the gain is taxable to the state: $80,000 x 5.3% = $4,240, instead of $10,600 at the full flat rate. Combined: roughly $40,240 before any NIIT, versus $46,600 without the deduction.

The planning takeaway: don't assume the flat rate is the whole story on an Idaho rental sale. Confirm Form CG eligibility before you model the deal, and if a 1031 exchange is on the table instead, weigh it against taking the gain now at the reduced effective rate.

Idaho ranked second in the nation for population growth in 2025, and the Boise metro area has been one of the fastest-growing markets in the West for several years running. Most of that growth is net migration, people moving in from other states, not births. A meaningful share of them are selling appreciated property somewhere else and buying or building in Idaho, or selling Idaho property they've held for years as values climbed.

For sellers relocating to Idaho, the flat 5.3% is usually a straightforward improvement over the top marginal rate in the states they're leaving. The planning trap is timing: states generally tax a gain based on where you were domiciled when the sale closed, not where you're headed. Establishing Idaho domicile well before a large sale closes matters more than the destination rate itself.

And whatever the exit looks like, a six-figure gain with no withholding usually triggers quarterly estimated payments, federal and Idaho both, due in the quarter of the sale rather than the following April.