Key takeaways
- Maine taxes S corporation income at the shareholder level, so the K-1s from the federal Form 1120-S carry the Maine numbers.
- An S corporation with a nonresident shareholder and Maine-source income files Form 941P-ME, even when nothing is withheld.
- Maine's pass-through entity tax (PTET) applies to tax years beginning on or after January 1, 2026, and the election is made on the return.
- The nonresident exemption affidavit and the composite agreement are collected from shareholders every year.
What Maine requires of an S corporation
Maine's Corporate Income Tax FAQ says subchapter S corporations with certain taxable gains must file Form 1120ME. That covers an S corporation that owes tax at the entity level, such as on built-in gains. A plain S corporation with no entity-level tax has no Form 1120ME to file, and I did not find a separate Maine S corporation information return in the pages I read. Confirm against the current Form 1120ME instructions before telling a client there is nothing to file.
What Maine does require is pass-through withholding. Under 36 M.R.S. 5250-B, an entity doing business in Maine withholds at the highest individual rate on each nonresident member's share of Maine-source income. The annual return is Form 941P-ME, filed electronically.
The third piece is new. For taxable years beginning on or after January 1, 2026, 36 M.R.S. 5199-C imposes a tax on any pass-through entity that elects into it.
Due dates for tax year 2026
Federal Form 1120-S for a calendar-year 2026 corporation is due March 15, 2027, a Monday, so there is no weekend shift this year. For tax year 2025 the instructions give March 16, 2026 because March 15 fell on a Sunday. Form 7004 requests the automatic 6-month extension and must be filed by the regular due date.
Rule 803 sets the Form 941P-ME due date at March 15 following the calendar year, so March 15, 2027 for tax year 2026. The rule allows an extension only when the entity has no withholding liability and received a federal information return extension. If the entity withheld anything, plan on no extension.
The PTET return and tax are due on or before the 15th day of the 3rd month after year end, March 15, 2027 for a calendar year, filed electronically. The election is declared on a timely filed return, including any extension, and is irrevocable after that due date.
Withholding estimates are due April 30, July 31, October 31 and January 31 of the following year, and are required when total withholding exceeds $1,000. Members get Form 1099-ME by January 31; it is not filed with Maine. PTET estimates are due on the 15th day of the 4th, 6th, 9th and 13th months: April 15, June 15, September 15 and January 15 for a calendar year. Check Maine's 2026 tax alerts for first-year installment relief before telling a client they missed one.
Nonresident shareholder withholding
Maine's FAQ gives 7.15% of the member's estimated Maine-source distributive income for individuals, estates and trusts, and 8.93% for members taxed as C corporations. An extra 2% applies above $750,000 for married filing separately, $1,000,000 for single filers, estates and trusts, and $1,500,000 for married filing jointly, head of household and qualifying surviving spouse.
Worked example for tax year 2026: a calendar-year S corporation has two nonresident individual shareholders at 50% each, and each one's Maine-source share is one hundred thousand dollars. Withholding is 7.15% of that, so 7,150 dollars per shareholder and 14,300 dollars in total. That exceeds $1,000, so estimates are required, each 25% of the lesser of 90% of the current year's required withholding or the prior year's required withholding.
No withholding applies to a nonresident with under $1,000 of Maine-source income, a tax-exempt member whose income is not taxable to the member, or a member who files Form 941AF-ME, the nonresident exemption affidavit. Exempt members are still reported on Form 941P-ME. A net-loss entity usually withholds nothing but still files it.
If the client says everyone is a Maine resident, ask for each shareholder's state of residence on December 31. A shareholder who moved mid-year is the usual miss.
Composite return for nonresident individuals
An entity may file a composite return for eligible nonresident individuals who agree. Each participant signs Form 941CF-ME, the Nonresident Member Affidavit and Agreement, every year. Rule 805 requires a new affidavit each year and says the entity keeps it at least six years after the composite return is filed.
Participants are listed on Schedule 3P of Form 941P-ME. A member left off Schedule 3P can have the affidavit revoked, and the entity must make estimated payments for the group if aggregate Maine income tax liability exceeds $1,000.
Decision rule: offer the composite when the nonresident shareholders have no other Maine income and would otherwise file a Maine individual return only for the K-1. Skip it for a shareholder with Maine wages or rental income, since that person files in Maine anyway.
The 2026 PTET election
The tax is the entity's pass-through entity taxable income times the highest marginal rate, excluding the individual surcharge, and chapter 822 credits cannot reduce it. Under 5199-B the election is annual, so a client who elects for 2026 decides again for 2027.
For nonresident qualified members, section 5199-D also requires estimated tax of 10% of the tax reported to each such member. The entity reports each member's share of tax, with name, taxpayer ID and resident or nonresident status, within 30 days after the Maine return due date, which is mid-April 2027 for a calendar-year 2026 return. The member credit sits in section 5219-CCC. I did not confirm the credit percentage on a primary page, so read the section before modeling owner results.
Before recommending the election, ask: Which shareholders are individuals, trusts or estates? Where does each live? Does the client pay PTET in other states, and how does each state credit it? Is anyone already over the federal SALT limit? Electing does not end the withholding and composite obligations; Maine's PTET presentation says the programs run alongside each other, so Form 941P-ME stays on the calendar.
Documents to collect from the client
For every S corporation client, ask for the shareholder roster with state of residence on December 31, any ownership change dates with the percentage held, the prior-year Form 941P-ME with its Schedule 3P, each shareholder's signed Form 941AF-ME or Form 941CF-ME, a summary of where services were performed or property sits, and any Form 1099-ME issued last year.
Wording that works: "Please list every shareholder and the state they lived in on December 31, 2026. If anyone moved during the year, include the move date." For the agreements, send: "Each nonresident shareholder must sign a new Form 941CF-ME or Form 941AF-ME this year, because last year's signature does not carry forward" and track it per shareholder.
For PTET: "Do you want us to model an entity-level Maine tax election for 2026? We need each owner's expected Maine-source income and other-state PTET payments by February 15, 2027." That date is your internal cutoff, not Maine's. In Usual, the residency questions and the per-shareholder affidavit uploads can sit in one recurring annual request per S corporation client.
Where firms slip
The most common error is skipping Form 941P-ME because the entity had a loss; the FAQ says it is still required. The second is treating last year's affidavit as current. The third is applying the federal extension to everything and missing that Form 941P-ME has no general extension.
The fourth is a PTET election made on an extended return while the payment was due earlier. The election can follow the extended return, but 5199-E sets the tax due date at the 15th day of the 3rd month, so schedule the payment before March 15, 2027 even if filing will be later.