How to Find and File Idaho Tax Form 40 for Your State Return

Filing state taxes in Idaho requires submitting Form 40, the standard document for reporting income, deductions, and credits. Accuracy is essential to avoid processing delays or penalties. Whether you’re a first-time filer or need a refresher, understanding how to complete and submit Form 40 can make tax season easier.

This guide explains how to obtain the form, fill out each section correctly, and submit it on time.

Filing Requirements

Idaho residents and part-year residents must determine if their income meets the state’s filing thresholds. In 2024, single filers under 65 must file if their gross income exceeds $13,850, while those 65 or older have a threshold of $15,700. Married couples filing jointly must file if their combined income surpasses $27,700, or $30,400 if both spouses are 65 or older. These amounts match Idaho’s standard deduction, which aligns with federal levels.

Nonresidents with Idaho-sourced income must file if their earnings exceed the prorated standard deduction based on their Idaho income percentage. For example, if a nonresident earns 40% of their total income from Idaho sources, they must file if that portion exceeds 40% of the standard deduction for their filing status. Common Idaho-sourced income includes wages from in-state employers, rental income from Idaho properties, and business earnings from operations within the state.

Self-employed individuals and independent contractors must file if their net earnings from Idaho exceed $400. Additionally, taxpayers who had Idaho income tax withheld but do not meet the filing threshold may still file to claim a refund. Those who owe use tax on untaxed online or out-of-state purchases must report it on their return, even if they have no other filing obligation.

How to Obtain the Form

Idaho Form 40 is available online as a downloadable PDF from the Idaho State Tax Commission’s website. Taxpayers who prefer electronic filing can use approved tax preparation software, which generates the form based on entered information and includes error checks to reduce mistakes.

For those needing a physical copy, Idaho’s tax offices provide paper forms upon request. Public libraries and some post offices may also stock tax documents during filing season, though availability varies. Taxpayers needing assistance can visit an Idaho Tax Commission office to ensure they obtain the correct form.

Sections of the Form

Idaho Form 40 consists of multiple sections, each serving a specific purpose in calculating state income tax liability. Completing each part accurately ensures compliance with Idaho tax laws and helps avoid errors that could lead to audits or delays.

Personal and Filing Status

The top portion of Form 40 requires basic identifying details, including the taxpayer’s full name, Social Security number, and mailing address. If filing jointly, a spouse’s information must also be included. Selecting the correct filing status—Single, Married Filing Jointly, Married Filing Separately, or Head of Household—is essential, as it determines the applicable standard deduction and tax brackets.

Idaho follows federal filing status rules, meaning taxpayers should generally use the same status as on their federal return. A married couple filing jointly on their federal return must do the same on their Idaho return unless they qualify for a separate filing election under Idaho law. Part-year residents and nonresidents must indicate their residency status and report only Idaho-sourced income. Errors in this section, such as selecting the wrong filing status, can lead to incorrect tax calculations and underpayment penalties.

Income Details

This section requires taxpayers to report all sources of income, including wages, self-employment earnings, rental income, and taxable interest. Idaho taxable income starts with federal adjusted gross income (AGI), transferred from the federal return. Idaho-specific additions and subtractions must then be applied to determine state taxable income.

Common additions include non-Idaho municipal bond interest and certain business deductions disallowed at the state level. Subtractions may include Idaho capital gains deductions, which allow a 60% exclusion on qualifying gains from Idaho-based assets held for at least one year. Taxpayers should also report any unemployment compensation, taxable Social Security benefits, and retirement income subject to Idaho tax. Discrepancies between federal and state income figures can trigger an audit or require an amended return.

Credits and Adjustments

Idaho offers various tax credits that can reduce the amount owed or increase a refund. The most commonly claimed credits include the Grocery Credit, which provides a refund for sales tax paid on food purchases, and the Idaho Child Tax Credit, which offers up to $205 per qualifying child. Other credits include the Credit for Taxes Paid to Another State, which prevents double taxation for residents earning income in multiple states, and the Earned Income Credit, a percentage of the federal Earned Income Tax Credit.

Adjustments to income may include deductions for health insurance premiums paid by self-employed individuals, contributions to Idaho’s 529 college savings plan, and certain military retirement benefits. These adjustments lower taxable income, reducing overall tax liability. Taxpayers should review eligibility requirements for each credit and deduction, as claiming ineligible benefits can result in penalties or additional tax assessments.

Other Important Lines

Form 40 also includes lines for reporting tax payments, penalties, and special tax obligations. Taxpayers must report any state income tax withheld from wages, estimated tax payments made throughout the year, and any extension payments submitted before the filing deadline. If total payments exceed the tax liability, the taxpayer is eligible for a refund; otherwise, the balance due must be paid by the filing deadline to avoid interest and late payment penalties.

This section also includes a line for reporting use tax, which applies to untaxed online or out-of-state purchases. Idaho law requires residents to self-report and pay use tax on items bought without sales tax. Failure to report use tax can result in penalties and interest. Additionally, taxpayers who owe more than $1,000 in state tax after withholding and credits may be subject to an underpayment penalty unless they meet safe harbor provisions under Idaho law.

Submitting the Completed Return

Once Form 40 is completed, taxpayers can file electronically or by mail. Electronic filing is generally preferred due to faster processing times and automatic error checking. The Idaho State Tax Commission partners with several tax preparation software providers that offer e-filing services, some of which are free for qualifying taxpayers. Those who owe a balance can pay through these platforms using direct debit or credit card payments, though card transactions may incur a processing fee.

For those mailing a paper return, the correct address depends on whether a payment is included. Returns with payments should be sent to the Idaho State Tax Commission’s designated payment processing address, while those expecting refunds or with no balance due are directed to a separate location. Taxpayers should include all necessary attachments, such as copies of W-2s and 1099s reflecting Idaho tax withholding, as well as any required supporting schedules. Missing documentation can result in processing delays.

Amending Your Filed Return

Mistakes on a tax return can happen, whether due to misreported income, overlooked deductions, or incorrect filing status. Idaho taxpayers who need to correct an error after submitting Form 40 must file an amended return using Idaho Form 40X. This form allows filers to adjust previously reported figures and provide explanations for the changes. Unlike federal amendments, which can be filed electronically in some cases, Idaho requires amended returns to be submitted by mail.

Form 40X requires taxpayers to enter the originally reported amounts alongside the corrected figures, with the difference calculated in a separate column. If the amendment results in additional tax owed, interest accrues from the original due date until payment is made. The Idaho State Tax Commission updates interest rates annually, with the 2024 rate set at 5%. If the correction leads to a refund, the state generally processes it within 10 to 12 weeks, though delays may occur if additional documentation is required.