Oklahoma C Corporation Tax Deadlines 2026

When is the C Corporation tax filing deadline in Oklahoma for 2026?

The Oklahoma C Corporation tax return is due Apr 15, 2026 for the 2026 tax year. An extension is available until Oct 15, 2026.

Does Oklahoma require C Corporation estimated tax payments?

Yes, Oklahoma 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 Oklahoma?

C Corporation entities in Oklahoma file using Form State corporate income tax return. You can download the form from Oklahoma Tax Commission at https://oklahoma.gov/tax.html.

Can I get an extension for my Oklahoma C Corporation tax return?

Yes. Oklahoma 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 Oklahoma?

Oklahoma 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 Oklahoma C Corporation taxes?

File through Oklahoma Tax Commission. Visit https://oklahoma.gov/tax.html for e-filing options, downloadable forms, and payment portals.