Key takeaways
- File an IA 1120S only if the S corporation has Iowa activity or Iowa-situs property. Iowa-resident shareholders alone do not create a filing.
- The 2026 calendar-year return is due April 30, 2027, and an S corporation that owes no Iowa tax gets an automatic six-month extension to file.
- A composite return for nonresident shareholders is a separate IA PTE-C, and its tax is due on the original date even when the filing is extended.
- A PTET election replaces the composite return for that year, is irrevocable, and carries estimated-payment duties.
What Iowa requires from an S corporation
The Department's 2025 instructions say an S corporation doing business in Iowa, or deriving income or loss from property with a situs in Iowa, must file an IA 1120S. It should not file if its only connection to Iowa is that a shareholder lives there.
A complete filing has the IA 1120S with schedules, an Iowa Schedule K-1 for every person who was a shareholder at any point in the year, and a copy of the federal Form 1120-S without the federal Schedules K-1. Every Iowa S corporation completes Schedule E, the Business Activity Ratio, even if all its business is in Iowa. It also needs an Iowa pass-through representative each year; changing one takes an IA 8979, not an amended return. An S corporation that owns 100% of a disregarded entity adds IA Schedule DE (41-179).
Due dates for tax year 2026
Iowa's rule is the last day of the fourth month after the year ends, so April 30, 2027 for a calendar-year 2026 return. The federal Form 1120-S comes first, on March 15, 2027, and Form 7004 extends only the federal filing.
Iowa's extension needs no form. An S corporation that owes no Iowa tax gets six months automatically, to October 31, 2027, a Sunday. The composite instructions refer to Iowa Code section 421.9A for weekend dates, and my reading is that it moves to Monday, November 1, 2027. The instructions do not state that date, so confirm it before it goes on a client calendar.
If the corporation makes the PTET election or owes built-in gains or passive income tax, the extension holds only when at least 90% of the total tax was paid by April 30, 2027. Otherwise it is late from May 1.
The composite return for nonresident shareholders
Under Iowa Code section 422.16B, an S corporation with nonresident shareholders files an IA PTE-C and pays Iowa tax for them, unless it made a timely PTET election or fits an exemption. The IA 1040C is discontinued for years beginning on or after January 1, 2022. Nonresident means an individual who is not an Iowa resident, an estate or trust without an Iowa situs, or an entity without an Iowa commercial domicile. A shareholder whose residence the entity does not know is treated as a nonresident.
The IA PTE-C follows the IA 1120S due date, extension included. The tax does not: it is due April 30, 2027 for 2026, and the Department's own example says extending the filing leaves the payment date alone. Estimated composite payments are allowed but not required.
The Department's composite guidance multiplies each nonresident member's Iowa-source income by the top Iowa rate for that member. For a nonresident individual in 2026 that is the flat 3.8% the Department announced. I could not read the PTE-C rate table, so check it on the form for corporate or trust shareholders.
Mixed residents, worked example. Iowa-source income is $300,000. Ann, an Iowa resident, owns 40% and stays out of the composite; she reports $120,000 on her own IA 1040. Ben, in Nebraska, owns 35%: $105,000 times 3.8% is $3,990. Cal, in Illinois, owns 25%: $75,000 times 3.8% is $2,850. The composite tax is $6,840 due April 30, 2027. If Cal signs form 41-175, nothing is paid for Cal, but the PTE-C is still filed because Ben has positive Iowa income.
The entity cannot ask for a refund after the first IA PTE-C is filed; a nonresident shareholder who overpaid claims it on that shareholder's own Iowa return.
The PTET election and what it costs in administration
Iowa Code section 422.16C lets an S corporation pay Iowa tax at the entity level. The election is irrevocable, covers one tax year, and is due six months after the original IA 1120S due date, October 31, 2027 for 2026 with the same weekend caveat. An electing entity files no IA PTE-C that year. Disregarded entities cannot elect, and no net operating loss or QBI deduction applies against the tax.
Worked example on the 2025 form: Part 4, line 27 shows $500,000 of Iowa-source items. At 3.8%, net PTET is $19,000. Shareholder credits are 96.2% of that, $18,278 (allocated in the same ratio as taxable income). Iowa's flat individual rate stays 3.8% for 2026, so expect the same rate, but confirm it on Part 6 of the 2026 form.
The credit reaches the shareholder through the shareholder's own Iowa return. For tax year 2022 that was Schedule CC (41-178), with "(PTET)" after the entity's name, flowing to IA 1040, line 62. For 2023 and later the Department says the procedure will appear in the return instructions, so I cannot give the 2026 line. Check the 2026 IA 1040 instructions.
The cost is cash timing. A calendar-year entity expecting more than $1,000 of PTET owes installments on April 30, June 30, September 30 and December 31. The prior-year safe harbor is unavailable without a prior-year PTET election, so a client who elected for 2025 may use it and a first-time elector cannot. IA 2220 computes the penalty. For a first-time 2026 election the last installment is December 31, 2026, so raise it now.
Penalties and e-filing
On the 2025 form, built-in gains and passive income are taxed at 5.5% up to $100,000 of income and 7.1% less $1,600 above it. I could not confirm those figures for 2026.
Late payment is 5% of unpaid tax if less than 90% was paid by the original date. For a corporation with no tax and no PTET election that files after the extended date, the imputed penalty is Iowa-source items times 3.8%, less credits, times 5%, capped at $25,000, with a $200 floor. On $400,000 of items that is $15,200 times 5%, or $760. On $20,000 it is $38, so the $200 floor applies.
MeF is mandatory with $250,000 or more in gross receipts, 10 or more Iowa K-1s, or $25,000 or more in Iowa credits on Schedule B. A paper return is then invalid unless the Department granted an exception on form 78-641 first.
If the 2026 instructions are not out when you prepare
Prepare on the 2025 instructions and treat three things as open: the PTET and composite rate lines, the built-in gains rate, and the line where owners claim the PTET credit. Label draft figures "2025-form basis" and recompute on the 2026 form before filing. Do not let an estimate payment wait for the forms.
Documents to collect and what to send
Ask for the shareholder roster for the whole year with each person's state of residence on the last day, mid-year transfers, and percentage owned per period. A roster without residence makes every owner a nonresident by default. For each nonresident, ask about other Iowa income and whether a signed 41-175 exists.
Also collect the federal Form 1120-S as filed, Iowa-source income and receipts by location for the Business Activity Ratio, Iowa credits, prior-year IA PTE-C and PTET election records, and dated Iowa estimates. If the corporation paid entity-level tax to another state, get that state's schedule; Iowa-resident shareholders need it for the IA 130 credit.
Wording for the client: "Please send every shareholder who held stock at any time in 2026, the state where each lived on December 31, the dates and percentages of any change, and a signed 41-175 for any owner who agreed to file their own Iowa return".