Idaho Business Tax Deadlines (2026)
Next: June 15, 2026 — Federal & Idaho Q2 Estimated Tax Payment
Next Deadline: June 15, 2026 — Federal & Idaho Q2 Estimated Tax Payment
Federal Tax Deadlines (2026)
| Form | Who Files | Due Date | Extension Deadline |
|---|---|---|---|
| Form 1040 (Schedule C) | Sole proprietors | April 15 | October 15 |
| Form 1065 | Partnerships, Multi-member LLCs | March 15 | September 15 |
| Form 1120-S | S-Corporations | March 15 | September 15 |
| Form 1120 | C-Corporations | April 15 | October 15 |
| Form 990 | Nonprofits | May 15 | November 15 |
| Estimated Taxes (Q1) | All | April 15 | — |
| Estimated Taxes (Q2) | All | June 15 | — |
| Estimated Taxes (Q3) | All | September 15 | — |
| Estimated Taxes (Q4) | All | January 15, 2027 | — |
Idaho State Tax Deadlines (2026)
| Tax Type | Due Date | Form/Filing | Notes |
|---|---|---|---|
| Individual Income Tax | April 15 | Form 40 | Flat 5.695% rate |
| Corporate Income Tax | April 15 | Form 41 | Flat 5.695% rate |
| S-Corp Return | March 15 | Form 41S | Pass-through entity |
| Partnership Return | March 15 | Form 65 | Pass-through entity |
| Sales Tax (Monthly) | 20th of following month | Via TAP | State rate 6% |
| Withholding Tax (Monthly/Quarterly) | Varies by payroll | Form 910 / 967 | Employers |
| Annual Report | Anniversary of formation | Filed with Secretary of State | No fee for most entities |
| Estimated Income Tax (Q1) | April 15 | Form 51 / 41ES | — |
| Estimated Income Tax (Q2) | June 15 | Form 51 / 41ES | — |
| Estimated Income Tax (Q3) | September 15 | Form 51 / 41ES | — |
| Estimated Income Tax (Q4) | January 15, 2027 | Form 51 / 41ES | — |
Quarterly Estimated Tax Deadlines in Idaho
Idaho follows the federal estimated tax payment schedule:
Estimated payments are required if you expect to owe $1,000 or more (individual) or $500 or more (corporate) in Idaho income tax.
Idaho-Specific Tax Requirements
Idaho has a flat income tax rate of 5.695% for both individuals and corporations, simplified from the previous graduated rate structure. This flat rate applies to all taxable income and uses federal taxable income as the starting point with Idaho-specific adjustments. Idaho does not have a separate franchise tax or gross receipts tax.
Idaho's state sales tax rate is 6% with no local sales taxes — the rate is uniform statewide, which simplifies compliance considerably. Groceries are taxed at the full rate in Idaho, which is unusual. The economic nexus threshold for remote sellers is $100,000 in sales. Businesses file sales tax returns through the Taxpayer Access Point (TAP), typically monthly or quarterly.
Annual reports are filed with the Idaho Secretary of State on the anniversary of the entity's formation date. There is no filing fee for most business entities, which is unusual. Idaho requires employers to withhold state income tax and file returns based on payroll size. The state has a relatively straightforward tax structure compared to many western states.
What Happens If You Miss an Idaho Tax Deadline?
Idaho State Tax Commission
Get Your Books Ready Before Tax Season
Idaho's flat tax and uniform sales tax rate keep things simple, but you still need accurate books to file on time. Don't let messy QuickBooks turn a simple filing into a headache.
> Books behind before a deadline? Ketchup catches up your QuickBooks in 3–7 business days — so you file on time with clean books. Get your price →
Related Resources
Behind on Idaho taxes?
Accounting Ketchup catches up your QuickBooks so you can file on time.