Idaho C Corporation Tax Deadlines 2026
Complete guide to C Corporation filing dates, extensions, estimated payment schedules, and required forms in Idaho for the 2026 tax year. Idaho imposes a state income tax, so C Corporation entities must file both federal and state returns.
Idaho C Corporation filing deadline
Calendar-year due date follows federal timing for corporations.
Due: Apr 15, 2026
Extension: Oct 15, 2026
Form: State corporate income tax return
Estimated payments
Quarterly estimated payment dates: Apr 15, 2026, Jun 15, 2026, Sep 15, 2026, Dec 15, 2026.
Due: Apr 15, 2026
Idaho C Corporation 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 | Dec 15, 2026 |
FAQ
When is the C Corporation tax filing deadline in Idaho for 2026?
The Idaho C Corporation tax return is due Apr 15, 2026 for the 2026 tax year. An extension is available until Oct 15, 2026.
Does Idaho require C Corporation estimated tax payments?
Yes, Idaho requires estimated tax payments for C Corporation entities. The quarterly due dates are: Apr 15, 2026, Jun 15, 2026, Sep 15, 2026, Dec 15, 2026. Penalties may apply if you underpay or miss a deadline.
What form do I file for a C Corporation in Idaho?
C Corporation entities in Idaho file using Form State corporate 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 C Corporation tax return?
Yes. Idaho allows an extension for C Corporation 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 C Corporation 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 →