The 2026 Oklahoma Tax Filing Season Opened January 26. Here's Your Checklist If You Own a Business.

The Oklahoma Tax Commission opened the 2025 income tax filing season on January 26, 2026, coordinated with the IRS. The deadline to file your 2025 Oklahoma return is April 15, 2026. Extensions are available — but an extension to file is not an extension to pay. If you owe and don't pay by April 15, the OTC will assess a 10% penalty on the unpaid amount plus interest from the due date.

For Oklahoma business owners, here are the items that generate the most errors, amendments, and headaches — in order of frequency from my practice.

1. Pass-Through Entity Tax (PTET) Election

Oklahoma allows pass-through entities (S-Corps, partnerships, LLCs) to elect to pay state income tax at the entity level. This was enacted as a workaround to the federal $10,000 SALT cap on individual returns. If your entity made the PTET election for 2025, the tax is paid on the entity's Oklahoma return and each owner claims a credit on their individual return. If your CPA filed the entity return but forgot the PTET election, or made the election but didn't flow the credit through to the individual returns, you're going to have a reconciliation problem.

2. Nonresident Withholding

If your Oklahoma partnership or S-Corp has nonresident owners, the entity is required to withhold Oklahoma income tax on those owners' distributive shares under 68 O.S. § 2385.29. The withholding is remitted to the OTC with the entity's return. Failure to withhold subjects the entity (not the nonresident owner) to penalties. I see this missed constantly in multi-state entities where the Oklahoma operations are managed by an out-of-state accounting firm that doesn't know the Oklahoma rules.

3. Depreciation Conformity

Oklahoma generally conforms to federal depreciation rules, including bonus depreciation. For 2025 returns (tax year 2025), the federal bonus depreciation rate was 60%. The OBBBA subsequently restored 100% bonus depreciation for property placed in service after January 19, 2025, but this applies prospectively — meaning the 2025 return is subject to the transition rules. If your business placed significant equipment in service in 2025, the depreciation calculation requires attention to the exact placed-in-service date relative to the OBBBA enactment.

4. Estimated Payment Reconciliation

If you made estimated Oklahoma income tax payments during 2025, verify that all four quarters are reflected on your OkTAP account before filing. I had a client last year who mailed a $14,000 estimated payment that the OTC never posted. We caught it on review, but if we hadn't, the return would have shown a $14,000 balance due that he'd already paid.

Your 2025 Oklahoma return is not the time to wing it. If you own a business, have pass-through income, or have any multi-state complexity, get professional help. The cost of preparing the return correctly is a fraction of the cost of amending it later — or defending it in an OTC audit.