Idaho Sole Proprietorship Tax Deadlines 2026
Complete guide to Sole Proprietorship filing dates, extensions, estimated payment schedules, and required forms in Idaho for the 2026 tax year. Idaho imposes a state income tax, so Sole Proprietorship entities must file both federal and state returns.
Idaho Sole Proprietorship filing deadline
Conforms to the federal calendar-year due date unless the state announces relief.
Due: Apr 15, 2026
Extension: Oct 15, 2026
Form: State income tax return
Estimated payments
Quarterly estimated payment dates: Apr 15, 2026, Jun 15, 2026, Sep 15, 2026, Jan 15, 2027.
Due: Apr 15, 2026
Idaho Sole Proprietorship Tax Calendar at a Glance
| Event | Date |
|---|---|
| Filing deadline | Apr 15, 2026 |
| Extension deadline | Oct 15, 2026 |
| Q1 estimated payment | Apr 15, 2026 |
| Q2 estimated payment | Jun 15, 2026 |
| Q3 estimated payment | Sep 15, 2026 |
| Q4 estimated payment | Jan 15, 2027 |
FAQ
When is the Sole Proprietorship tax filing deadline in Idaho for 2026?
The Idaho Sole Proprietorship tax return is due Apr 15, 2026 for the 2026 tax year. An extension is available until Oct 15, 2026.
Does Idaho require Sole Proprietorship estimated tax payments?
Yes, Idaho requires estimated tax payments for Sole Proprietorship entities. The quarterly due dates are: Apr 15, 2026, Jun 15, 2026, Sep 15, 2026, Jan 15, 2027. Penalties may apply if you underpay or miss a deadline.
What form do I file for a Sole Proprietorship in Idaho?
Sole Proprietorship entities in Idaho file using Form State income tax return. You can download the form from Idaho State Tax Commission at https://tax.idaho.gov.
Can I get an extension for my Idaho Sole Proprietorship tax return?
Yes. Idaho allows an extension for Sole Proprietorship returns until Oct 15, 2026. Note that an extension gives you more time to file, not more time to pay — any tax owed is still due by the original deadline of Apr 15, 2026.
What are the penalties for filing late in Idaho?
Idaho typically charges a failure-to-file penalty (usually 5% of unpaid tax per month, up to 25%) and a failure-to-pay penalty (usually 0.5-1% per month). Interest also accrues on unpaid balances. Filing for an extension by the original deadline avoids the failure-to-file penalty but not the failure-to-pay penalty.
Where can I file Idaho Sole Proprietorship taxes?
File through Idaho State Tax Commission. Visit https://tax.idaho.gov for e-filing options, downloadable forms, and payment portals.
Idaho Estimated Tax Payments
View the full quarterly estimated payment schedule for Idaho, including all entity types and payment methods.
View Idaho estimated payments →