Idaho taxes

Idaho taxes personal income at a flat 5.3%, after a first slice taxed at nothing. A sole proprietor owes no separate business tax, and an LLC's only filing is a free annual report. Every corporation, S corporations included, pays at least $30 a year: a $20 minimum tax and a $10 building fund tax. C corporations pay 5.3% on the profit apportioned to Idaho.

Personal income tax

Idaho residents file Form 40, due April 15, 2026. You automatically get until October 15, 2026 to file, but only if you have already paid at least 100% of last year's Idaho tax or 80% of this year's by April 15, 2026.

The rate is a flat 5.3%, but the first $4,811 of taxable income is taxed at nothing, or the first $9,622 for married couples filing jointly, heads of household and qualifying surviving spouses.

Idaho uses the federal standard deduction, including the extra amounts for being 65 or older or blind, and it allows the federal qualified business income deduction. There is no personal or dependent exemption.

Return

Form 40

Due date

April 15, 2026, with an extension to October 15, 2026 if enough tax is paid on time

Rate

5.3% flat

Taxed at 0%

The first $4,811 single or married filing separately, $9,622 married filing jointly, head of household or qualifying surviving spouse

Standard deduction

The same as your federal standard deduction

Child tax credit

$205 for each child 16 or under at the end of 2025

Food tax credit

$155 for each person in the household, and refundable

Not taxed

Social Security and Railroad Retirement

Sole proprietor

A sole proprietor with no LLC files nothing with Idaho for the business. The Secretary of State annual report is only for registered entities.

Your business profit is taxed on your own Form 40, at the flat 5.3%.

Single-member LLC

Every Idaho LLC files an annual report with the Secretary of State in its anniversary month, however few members it has. Filed online it costs nothing. A paper filing adds a $20 processing charge, which you can avoid by filing online.

The report only confirms the company's details, but letting it lapse is how an LLC falls out of good standing. The LLC's profit is taxed on your own Form 40.

Partnership

An Idaho partnership files Idaho Form 65, the partnership return of income, and lists every owner by name on Form PTE-12.

For each partner who is a nonresident individual, the partnership must settle that partner's Idaho tax one of three ways: withhold and pay it on Form PTE-01, include the partner in a composite return it files and pays for, or hold a signed agreement that the partner will file their own Idaho return. Doing nothing is not an option. The composite route also brings a $10 permanent building fund tax for each nonresident individual included. A partnership whose partners all live in Idaho pays none of it.

Like every registered Idaho business, it files the free annual report.

S corporation

An Idaho S corporation files Idaho Form 41S. Unlike most states, Idaho charges every S corporation its $20 minimum tax, whether or not it has any income taxed at the corporate level, plus the $10 permanent building fund tax. So an S corporation owes at least $30 a year.

The same three-way rule applies to shareholders who live outside Idaho: withhold, include them in a composite return, or hold their signed agreement. It also files the free annual report.

C corporation

A C corporation files Idaho Form 41 and pays 5.3% of the income apportioned to Idaho, never less than $20. A corporation selling into other states counts its Idaho share by sales alone by default. Some industries, such as electrical and telephone companies, construction contractors, airlines, trucking and financial institutions, may elect to use property, payroll and sales instead.

It also pays the $10 permanent building fund tax on its own line, on top of the income tax. So a corporation that did nothing all year still owes $30. It files the free annual report as well.

Return

Idaho Form 41

Corporate income tax

5.3% of Idaho taxable income, minimum $20

Permanent building fund tax

$10, on top of the income tax

Multi-state profit

Idaho sales over total sales, unless an eligible industry elects three factors

Annual report

Free online

Estimate your state tax

Pick your business type and enter this year's numbers to see the state business tax Idaho charges. It assumes all your sales are in Idaho.

An estimate for planning, not tax advice.

Sources

• Idaho 2025 Form 40 instructions (EIN00046), Form 40 (EFO00089) and Form 39R (EFO00088), tax.idaho.gov
• sos.idaho.gov Annual Report Help (filing requirement, online filing, $20 manual processing fee)
• sos.idaho.gov Business Forms
• tax.idaho.gov Form 41 instructions, 2025 (EIN00044): "Minimum Tax. The minimum tax of $20 is required for each corporation"; the $10 permanent building fund tax
• tax.idaho.gov Form 41S instructions, 2025: "The total tax before credits can't be less than $20"
• tax.idaho.gov Form 65 instructions, 2025 (EIN00045): "the $10 PBF tax for each nonresident individual partner"; Form PTE-12 composite reporting
• tax.idaho.gov Form 41 (EFO00025, 03-02-2026), line 38: "Idaho income tax. Multiply line 37 by 5.3%. Minimum $20 for each corporation"
• tax.idaho.gov Form 42 instructions (EIN00099, 06-25-2025): "Single-sales apportionment is the default apportionment method", and the industries that may elect three factors

Last reviewed August 2026.