State & Local Tax (SALT)
State Tax Deadlines
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Oklahoma Tax Deadlines at a Glance (2026)
Entity Type | Return Due | Extension Deadline |
|---|---|---|
Individuals | April 15, 2026 | October 15, 2026 |
C Corporations | May 15, 2026 | November 16, 2026 |
S Corporations | March 16, 2026 | September 15, 2026 |
Partnerships | March 16, 2026 | September 15, 2026 |
Businesses
Oklahoma allows C corporations 30 days beyond the federal due date: the calendar-year corporate return (Form 512) is due May 15, 2026. Oklahoma also requires withholding on nonresident owners unless a composite return is filed.
Estimated Taxes
Quarter | Due Date |
|---|---|
Q1 | April 15, 2026 |
Q2 | June 15, 2026 |
Q3 | September 15, 2026 |
Q4 | January 15, 2027 |
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