Key takeaways
- Florida's base for an S corporation is the amount subject to federal tax under IRC section 1374 or 1375, under section 220.13(2)(i) of the Florida Statutes.
- Check line 23a and line 23b of the federal Form 1120-S before deciding that no Florida return is needed.
- For tax year 2026, a calendar-year Florida return is due May 1, 2027, and a six-month extension runs to November 1, 2027.
- A federal extension alone is not enough for Florida. The tentative return and the estimated payment are still due May 1, 2027.
What Florida taxes on an S corporation
Florida's corporate income tax starts from the federal S corporation rules and then stops almost immediately. Section 220.13(2)(i) of the Florida Statutes says that for a corporation with an S election under IRC section 1362(a), taxable income means the amounts subject to tax under IRC section 1374 or section 1375 for each taxable year. The ordinary profit that passes through to shareholders on the federal Form 1120-S is not in that definition.
The rate is 5.5 percent of net income under section 220.11(2)(a). If an S corporation has no built-in gains tax and no excess net passive income tax, the statutory base is zero and there is no Florida corporate income tax to pay.
The federal return still decides the question. The Florida base is read from the built-in gains and passive income amounts on the 2026 Form 1120-S, so the firm has to pull those numbers from the federal return before it can answer the state question.
When the F-1120 is required
The return is the Florida Corporate Income/Franchise Tax Return, Form F-1120. The Department of Revenue lists it by reference in rule 12C-1.051 of the Florida Administrative Code as Ref-18772 F-1120. A notice dated 9/30/2026 proposes to adopt revisions to the F-1120, so pull the 2026 form and instructions when preparing the return and do not reuse last year's copy.
Two federal triggers feed the Florida base. The first is the built-in gains tax under IRC section 1374. It applies to a corporation that holds assets with built-in gain from its time as a C corporation and recognizes that gain during the recognition period after the S election. The 2025 federal instructions put that tax on line 23b of Form 1120-S, which comes from line 23 of Part III of Schedule D.
The second trigger is the excess net passive income tax under IRC section 1375. The 2025 federal instructions compute it on line 23a, where the worksheet multiplies line 10 by 21 percent (0.21). This tax matters mainly for a former C corporation that still carries accumulated earnings and profits and has large passive investment income.
Decision rule for the 2026 return
Open the 2026 Form 1120-S and go to line 23a and line 23b, which carry the federal tax under sections 1375 and 1374. If both lines show zero, the Florida base is zero under section 220.13(2)(i) and no Florida corporate income tax is due.
If either line shows an amount, file the 2026 Form F-1120. For a built-in gains amount, ask the client for the conversion date from C corporation to S corporation and the asset list at conversion, so you can confirm which assets were held with built-in gain and whether the recognition period has ended. For an excess passive income amount, ask for the last C corporation return and the accumulated earnings and profits figure from it.
A zero-tax S corporation with no line 23a or 23b amount can still raise a filing question. The statute gives no Florida base in that case. I could not confirm on a primary source whether the Department still expects a zero-tax F-1120 to be filed. Read the 2026 F-1120 instructions before you put 'no Florida return' in the workpapers.
What the Florida tax costs when it applies
Worked example for tax year 2026. A Florida S corporation has $100,000 of built-in gains tax base under IRC section 1374. Under section 220.13(2)(i), that $100,000 is the Florida taxable income. At 5.5 percent, the Florida tax is $5,500 before any exemption, credit or adjustment that the 2026 F-1120 allows.
I did not verify an exemption amount for the F-1120, so do not net one out until the 2026 instructions are open. Record the Florida figure in the same workpaper as the federal built-in gains computation, so the two numbers tie to the same Schedule D line and a reviewer can trace both in one place.
Due dates and the extension
Section 220.222(1)(a) says that returns not covered by the special rules are due on or before the 1st day of the 5th month after the close of the taxable year. For a calendar year, the 5th month after December is May, so the 2026 Florida return is due May 1, 2027.
The Florida due date comes after the federal one. The 2025 federal instructions show March 16, 2026 for calendar-year 1120-S returns, because March 15 fell on a Sunday. The 2026 federal return is due in March 2027, and the Florida return follows in May.
Section 220.222(2)(a) extends the due date until six months from the original due date. For a calendar-year 2026 return, that is November 1, 2027. The extension depends on a federal extension and on the requirements of section 220.32. Section 220.32(1) requires a tentative return and payment of the estimated balance on or before the original due date, which is May 1, 2027. The statute does not name the extension form, so pull the current form from the Department of Revenue forms library before filing.
Penalties and what the payment deadline means
Section 220.32(3) says that interest is payable under section 220.809 and that a penalty is determined at the rate of 12 percent per year on an underpayment. A client who files the extension on November 1, 2027 but pays the tax later is exposed to that penalty from the original date.
Treat May 1, 2027 as the payment deadline for any Florida tax, even when the return itself is extended. The return extension does not move the payment date.
Failure modes and fixes
Failure: the preparer files the federal 1120-S, sees no state tax line on the summary and skips the Florida question. Fix: add a line 23a and line 23b check to the Florida workpaper for every S corporation client, whether the answer is zero or not, so the file records the answer.
Failure: the client converted from a C corporation years ago and assumes the built-in gains period has ended. Fix: pull the conversion date and the asset list at conversion before deciding, and write the recognition period analysis into the workpaper.
Failure: the firm files the Florida extension on the strength of the federal extension alone. Fix: confirm the tentative return and the estimated payment went in by May 1, 2027, and keep the proof of filing with the return.
Failure: the annual report and the income tax return get merged into one deadline. The annual report is a Division of Corporations filing and is separate from the Department of Revenue return. Fix: keep the two deadlines on separate lines of the client calendar.
Open items before you file
Three points in this guide need a check against the 2026 forms before the return is prepared. The first is the exemption amount, if any, on the F-1120. The second is whether a zero-tax S corporation must still file, which the 2026 instructions answer. The third is the extension form, because the statute does not name it.
The 1375 rate of 21 percent comes from the 2025 federal instructions. The built-in gains tax rate under section 1374 is not stated in the lines I read, so confirm it in the 2026 federal instructions before putting a rate in a client memo.