Idaho Income Tax 2026: Brackets, Rates & Calculator

Q: "What is Idaho's income tax rate for 2026?"

"A flat 5.3% on taxable income above an annually adjusted zero-rate threshold — unchanged from 2025. Idaho switched from graduated brackets to a flat tax in 2023."

Q: "Does Idaho have a standard deduction?"

"Yes — Idaho uses the federal standard deduction: $16,100 for single and married filing separately, $32,200 for married filing jointly, and $24,150 for head of household in 2026."

Q: "Do Idaho cities charge income tax?"

"No. No Idaho city or county levies a local income tax, so the state Form 40 is your only state income return."

Q: "What is Idaho's $10 Permanent Building Fund tax?"

"A flat $10 charge Idaho adds to most individual income tax returns to fund state buildings. It applies regardless of income unless you receive public assistance."

October 16, 2026 · 5 min read · By the DollarWise team

Idaho Income Tax 2026: Brackets, Rates & Calculator

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Idaho keeps it simple: one flat rate, no brackets to climb, no marginal-rate math. For 2026, that rate is 5.3% — unchanged from 2025 — applied to taxable income above a small inflation-adjusted threshold. This guide explains exactly how Idaho’s flat tax works, what you can deduct, and how to estimate what you’ll owe.

For the federal side of your return, use our free US federal income tax estimator alongside this Idaho guide. (A dedicated Idaho calculator is on the roadmap.)

Idaho’s flat tax: how it works

Idaho abandoned its graduated brackets in 2023, switching to a flat 5.8% rate. The rate then fell to 5.695% for 2024 and 5.3% for 2025, where it remains for 2026. One rate, everyone, same math.

But “flat” doesn’t mean “every dollar from dollar one.” Idaho taxes income above an annually inflation-adjusted threshold at 5.3%, while income below that threshold is taxed at 0% — effectively a zero bracket built into the flat system. Deductions (standard or itemized) reduce your taxable income before the rate applies, so the threshold and deductions work together to shield lower incomes.

The practical upshot: a single filer with modest income may owe little or nothing, while every additional dollar above the threshold costs exactly 5.3 cents — no bracket jumps, no surprises, the same marginal rate whether you earn $50,000 or $500,000.

Deductions: what reduces your Idaho taxable income

Standard deduction. Idaho conforms to the federal standard deduction, which for 2026 is $16,100 for single and married filing separately, $32,200 for married filing jointly, and $24,150 for head of household. These adjust annually for inflation.

Itemized deductions. If your itemized deductions (mortgage interest, charitable gifts, state and local taxes up to the federal SALT cap, etc.) exceed the standard amount, itemizing lowers your Idaho taxable income further. Idaho generally follows federal itemized rules.

Above-the-line adjustments. Contributions to HSAs, traditional IRAs, student loan interest, and similar federal adjustments reduce the income Idaho starts from, since Idaho begins its calculation with federal adjusted gross income.

Estimating your Idaho tax (worked example)

Say you’re single, earn $80,000 in wages, and take the 2026 standard deduction:

Subtract the standard deduction: $80,000 − $16,100 = $63,900 of income subject to Idaho tax (before the zero-bracket threshold, which shields a bit more).
Apply the flat rate: roughly $63,900 × 5.3% ≈ $3,387 (slightly less after the zero-rate threshold).
Add the $10 Permanent Building Fund tax → ≈ $3,397 total.
Effective rate: about 4.2% of gross income — well below the 5.3% statutory rate, thanks to the deduction and zero bracket.

The lesson: the flat rate applies to taxable income, not gross income. Deductions and the zero threshold mean your effective rate always lands below 5.3%.

Idaho tax facts worth knowing

No local income taxes. Boise, Meridian, Coeur d’Alene — no Idaho city or county taxes income. Form 40 is your only state income return, which keeps compliance blissfully simple.

The $10 Building Fund tax. Most individual returns include a flat $10 Permanent Building Fund charge for state buildings. It’s tiny, it’s nearly universal, and it surprises first-time filers — now you won’t be surprised.

Estimated payments. If you’ll owe $1,000+ beyond withholding, Idaho expects quarterly estimated payments (Form 51): April 15, June 15, September 15, and January 15. Freelancers and landlords, take note — the flat rate makes estimating easy (5.3% of expected taxable income, divided by four).

Competitive overall. The Tax Foundation ranks Idaho’s tax system 9th nationally for 2026 competitiveness — the flat income tax, moderate 6% sales tax, and low property taxes combine into one of the friendlier tax climates in the West.

Withholding uses 5.3% too. Idaho’s 2026 withholding tables apply the same 5.3% rate, so your paycheck withholding should track your actual liability closely if your W-4 is accurate.

Filing basics. Idaho individual returns are filed on Form 40 with the State Tax Commission, due April 15. Because the state starts from federal AGI, most filers complete their federal return first — then the Idaho portion is a short, simple calculation: subtract deductions, apply 5.3%, add the $10 fund tax. E-filing is free through the state’s online portal and typically processes refunds within a few weeks.

Frequently asked questions

What is Idaho’s income tax rate for 2026?

A flat 5.3% on taxable income above an annually adjusted zero-rate threshold — unchanged from 2025. Idaho switched from graduated brackets to a flat tax in 2023 (5.8%), cut it to 5.695% for 2024, then to 5.3% for 2025–2026.

Does Idaho have a standard deduction?

Yes — Idaho uses the federal standard deduction: $16,100 (single/MFS), $32,200 (married filing jointly), $24,150 (head of household) for 2026. Estimate the federal side with our free US federal income tax estimator.

Do Idaho cities charge income tax?

No. No Idaho city or county levies a local income tax, so the state Form 40 is your only state income return. Withholding, estimates, and filing are all state-level.

What is Idaho’s $10 Permanent Building Fund tax?

A flat $10 charge Idaho adds to most individual income tax returns to fund state buildings. It applies regardless of income unless you receive public assistance — small, but it catches first-time filers off guard.

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Written by the DollarWise team

We turn confusing money topics into plain-English guides for beginners. Every article is written to be actionable on day one — no jargon, no hype, no sales pitch.