Key takeaways
- An S corporation engaged in business or deriving income from Oklahoma property files Form 512-S, never Form 512.
- The Oklahoma return is due 30 days after the federal due date, and electronic filing is required.
- A federal extension covers the Oklahoma return only if no Oklahoma tax is owed.
- Nonresident shareholders trigger 4.75% withholding on the 2025 packet unless the entity elects to pay tax itself on Form 586 or holds a signed Form OW-15.
- Oklahoma franchise tax no longer applies from tax year 2024.
Which return Oklahoma wants
The Oklahoma Tax Commission's packet says any corporation with a Subchapter S election in effect that is engaged in business or derives income from property in Oklahoma, and that must file a federal Form 1120-S, files Form 512-S. The packet adds: do not use Form 512. That is the C corporation return.
The packet bundles Form 512-S, a supplemental schedule called Form 512-S-SUP, and Form 512-SA, the nonresident shareholder agreement. Attach a complete copy of the federal Form 1120-S with the Schedule K-1 for every shareholder. If the corporation skips Schedules L and M-1 federally, the packet asks for balance sheets or a financial statement instead, and warns that omissions can delay the shareholders' own returns.
Oklahoma franchise tax is no longer part of the picture. The Tax Commission states that tax year 2023 was the last year franchise returns were required, with no franchise filing requirement from tax year 2024. Delete any franchise line from the client's checklist.
Due date and extension for the 2026 return
The packet says the Oklahoma return is due 30 days after the due date set under the Internal Revenue Code. The federal rule is the 15th day of the 3rd month after year end. For tax year 2025 that was March 16, 2026, because the 15th fell on a Sunday. Calendar-year 2026 returns are due in mid-March 2027, and the Oklahoma return follows 30 days behind. A last day that falls when Tax Commission offices are closed moves to the next business day.
A valid federal extension, requested on Form 7004, automatically extends the Oklahoma due date, but only if no Oklahoma liability is owed. The IRS says that extension is generally 6 months and Form 7004 generally must be filed by the regular due date. Attach a copy to the Oklahoma return.
If the federal return was not extended, or Oklahoma tax is owed, the entity asks for an extension on Form 504-C, and PTEs use Form 504-PTE. The Tax Commission is explicit that an extension to file is not an extension to pay, and that an extension is valid only when 90% of the tax is paid by the original due date. Late payment brings a one-time 5% delinquent penalty and interest at 1.25% per month.
Ask the client in November: "Will any shareholder live outside Oklahoma, or will the company owe Oklahoma tax at the entity level this year? If either is yes, I need your year-to-date distributions so we can decide on an extension before the deadline." Send it in November, not March.
When the S corporation itself owes tax
Most S corporations owe nothing on Form 512-S. Entities paying tax at the corporate level must make estimated payments when the year's tax can reasonably be expected to reach $500 or more, with payments of at least 70% of the tax due or 100% of the prior year's liability. Underpayment interest runs at 20% a year, and none is charged if the tax shown on the return is under $1,000. The computation uses Form OW-8-P.
Decision rule: if the client is an electing PTE or pays nonresident tax for shareholders, put estimates on the calendar. If neither, Form 512-S is mostly an information return.
Nonresident shareholders: withholding or election
A pass-through entity must withhold Oklahoma income tax at 4.75% of the Oklahoma share of taxable income distributed to each nonresident shareholder, according to the 2025 packet. No withholding is required for a nonresident who gives the entity a signed Form OW-15, a withholding exemption affidavit that the Tax Commission describes as binding until the member revokes it. There is also no withholding on distributions to another PTE, on royalty income already withheld, or by an entity that elected to be a PTE.
Worked example for tax year 2025: an S corporation has Oklahoma net distributable income of $200,000 and a Texas shareholder who owns 40%. The shareholder's Oklahoma share is $80,000 and, if all of it is distributed, the entity withholds $3,800. With a signed Form OW-15 at distribution, withholding is zero.
Mechanics: register on Form OW-11, file and pay on Form WTP-10003 by the return's due date including extensions, give each nonresident a Form 500-B by that date and file copies electronically with cover Form 501. The shareholder attaches the Form 500-B to their Oklahoma return. If the entity expects to pay more than $500 it makes quarterly estimates on Form WTP-10005, unless it expects a loss or no distributions.
Check the rate before you compute for 2026. The 4.75% figure comes from the 2025 packet. Oklahoma passed House Bill 2764 in 2025 to change the individual rate structure for later years and tie further cuts to a revenue trigger, and the Tax Commission's 2026 packet is not yet out. Use the rate printed in that packet for 2026 distributions.
The electing PTE alternative
A PTE required to file an Oklahoma S corporation return can elect on Form 586 to pay Oklahoma tax at the entity level. The election takes priority over the nonresident Form 512-SA and composite return requirements for the same year and removes withholding on distributions.
On the 2025 packet, each member's share of Oklahoma net entity income is taxed at 4.75% for individual and trust members and 4% for corporate, S corporation and partnership members. Using the example above, $200,000 of Oklahoma net entity income held by individuals produces entity tax of $9,500. The entity marks box 4 on page 1 of Form 512-S and computes the tax on Form 587-PTE. A first-year election marks box 5 and attaches Form 586.
Timing: the Tax Commission says the election goes in no later than two months and 15 days after the start of the taxable year, or, beginning with tax year 2024, with the timely filed return including extensions. Revocation cannot ride along with a return and must be filed separately on Form 586. Entities use Form EF-PTE for the separate balance-due payment, Form 504-PTE for the extension and Form OW-8-ESPTE for estimates from tax year 2025.
Members still act: each excludes the covered income on their own return and attaches a schedule listing the electing PTE, its FEIN and the OTC acknowledgement letter. Credits generated by the entity stay at the entity level.
Documents to collect from the client
Send this list with a deadline: the completed federal Form 1120-S and every Schedule K-1; a shareholder roster with state of residence and the date of any ownership change; the distribution ledger by shareholder and date; a signed Form OW-15 from any nonresident who wants no withholding; and property, payroll and sales by state if the company works outside Oklahoma.
Add what the packet asks for: municipal bond interest by source if the corporation is domiciled in Oklahoma, Forms 1099 for any excluded U.S. government interest, proof of Safety Pays participation for the $1,000 exemption, and poll-worker leave records for the $100-per-day exemption.
Exact wording: "Please upload a spreadsheet of every distribution this year, with date, amount and the shareholder's home state. We withhold Oklahoma tax on nonresident distributions unless a signed Form OW-15 is on file, so send those forms too." Track who has not replied.
Failure modes and fixes
A shareholder who moved mid-year: keep dated distribution ledgers and get the move date in writing. A paper filing: the packet cites Rule 710:50-17-1 requiring electronic filing, so confirm your software supports Oklahoma 512-S e-file before promising the return. A federal extension filed with Oklahoma tax owed: it fails unless 90% of the tax was paid by the original date, so pay first.
Federally, the Form 1120-S late-filing penalty for tax year 2025 was $255 per shareholder per month, up to 12 months, and $340 per late or incorrect Schedule K-1. Check the 2026 instructions for the amounts that apply to returns due in 2027.