Key takeaways
- File Form 5S for the corporation and Schedule 5K-1 for each shareholder; Form PW-1 goes with it whenever any shareholder is a nonresident.
- A calendar-year corporation's Form 5S is due March 15, 2027, and the Wisconsin-only extension runs seven months, to October 15, 2027.
- Nonresident shareholders with $2,000 or more of Wisconsin income from the corporation are subject to withholding unless an exemption applies.
- The entity-level tax election is made on Form 5S itself, by the extended due date, with consent from holders of more than 50% of the shares.
What the corporation files in Wisconsin
A Wisconsin tax-option corporation, the department's term for an S corporation, files Form 5S in addition to the federal Form 1120-S. The IRS describes Form 1120-S as the return reporting the income, gains, losses, deductions and credits of a domestic corporation with an S election. Wisconsin's counterpart to the federal shareholder statement is Schedule 5K-1.
Form PW-1 must be e-filed, and the department requires S corporations to e-file composite returns through the Federal/State E-Filing Program or My Tax Account. A hardship waiver is requested on Form EFT-102. A qualified subchapter S subsidiary files no separate Wisconsin return.
Due date and extension for tax year 2026
For a calendar-year corporation, Form 5S and Form PW-1 are both due March 15, 2027, a Monday. A due date on a weekend or holiday moves to the next business day.
Wisconsin gives an automatic seven-month extension, claimed by checking Item B on Form 5S and entering the extended due date. Seven months after March 15, 2027 is October 15, 2027. There is no state extension form to send.
If the client filed a federal extension on Form 7004, which the IRS describes as an automatic six-month extension, Wisconsin extends its date to 30 days after the federal extended date. Attach a copy of the federal extension when you file Form 5S, not before.
The extension covers filing only. Interest runs on tax not paid by the unextended due date, so a corporation that owes nonresident withholding should pay it in March even if the return goes on extension.
Penalties after the extended date
No late-filing fee applies within the extension period. After the extended due date, Form 5S carries a $150 late-filing fee, delinquent interest of 1.5% per month and a negligence penalty of 5% per month on the tax required to be shown, capped at 25%. Failure to withhold is also 5% per month, capped at 25%.
If the department rejects an e-filed return, you have five business days to fix it and resubmit to keep the original filing date. Assign rejection notices to a named person, not a shared inbox.
Withholding on nonresident shareholders and Form PW-1
A corporation with Wisconsin income allocable to a nonresident shareholder must withhold on it even if nothing is distributed. Form PW-1 reconciles the year, is due on the unextended due date of Form 5S, and must match the withholding shown on each Schedule 5K-1.
A nonresident whose Wisconsin income from the entity is under $2,000 is exempt from withholding. The line was $1,000 for taxable years beginning before January 1, 2024, so a workpaper template still carrying $1,000 is stale. A shareholder with $1,800 of Wisconsin-source income needs no withholding; one with $2,000 does. Test the figure from Schedule 5K-1, not the federal K-1.
Installments are due the 15th day of the 3rd, 6th, 9th and 12th months, so March 15, June 15, September 15 and December 15 for a calendar-year corporation. Each is 25% of 90% of current-year withholding or of prior-year withholding. At $8,000 expected withholding, the 90% method gives four installments of $1,800. Underpayments accrue interest at 12% per year.
On November 10, 2026 only the December 15 installment is still open for tax year 2026, so check now whether the earlier three were paid. The rate itself is printed on Form PW-1 and its instructions; take it from the final tax year 2026 version, not a prior-year workpaper.
Form PW-2 exemptions: who asks, and when
A nonresident shareholder avoids withholding by filing Form PW-2 through My Tax Account. For an S corporation it is due the last day of the first month after year end, so the last day of January 2027, which is a Sunday and therefore rolls to the next business day. A separate Form PW-2 is needed each year, and the department typically responds in about 30 days.
Keep the approval letter. The corporation still lists the shareholder on Form PW-1 and checks the box showing the affidavit was filed.
Send each nonresident shareholder something specific: "If you live outside Wisconsin and expect more than $2,000 of Wisconsin income from the company, tell us by December 15 whether you want to file a Form PW-2, join a composite return, or have us withhold." Each answer changes what the corporation pays in March.
Composite return on Form 1CNS
Form 1CNS lets the corporation file one Wisconsin return for two or more participating nonresident shareholders. For a calendar-year corporation it is due April 15, 2027. File Form PW-1 first, or shareholders may receive a bill.
Leave out anyone who was a Wisconsin resident for part of the year, has other Wisconsin taxable income, claims credits or itemized deductions, must file Schedule RT, expects to file Form 1NPR, has an approved Form PW-2, or is an electing small business trust. Entities that make the entity-level election cannot participate either.
Decision rule: if the shareholder has a Wisconsin rental, a K-1 from another Wisconsin entity, or wants an itemized deduction, send them to Form 1NPR. On Form 1CNS, column D1 takes net income from Schedule 5K-1 column e, column D2 takes gross income from line 20, and the same SSN cannot appear twice in column B. Attach only a schedule explaining differences from the K-1, such as an NOL carryforward.
The entity-level tax election
An S corporation can elect to pay Wisconsin tax at the entity level, so shareholders leave their share of its income out of Wisconsin adjusted gross income. Check box 7 in Part A of Form 5S, with consent from holders of more than 50% of the shares on the day of election. It is made each year, by the extended due date, which is October 15, 2027 for a calendar-year corporation.
The department does not require shareholder signatures but the corporation must prove consent if asked, so keep dated written consent. An amended Form 5S can add or revoke the election by the extended due date. Tell shareholders by checking box 3 in Part B of each Schedule 5K-1.
An electing entity is exempt from withholding on nonresidents, so decide before the installments are set. Whether it saves tax needs a model using the client's own numbers; the department's page does not answer that.
What to collect from the client
Ask for the shareholder list at December 31 with state of residence for each; each nonresident shareholder's other Wisconsin income; approved Form PW-2 letters; prior-year Form PW-1 and Form 5S; the March, June and September 2026 withholding payment confirmations; and written consent for any entity-level election.
Ask residency as a one-line question: "Did any shareholder change state of residence in 2026, and on what date?" A part-year resident cannot be in the composite return.
In Usual, a request per shareholder with an upload item for each Form PW-2 letter keeps exemption paperwork out of a shared email thread. A spreadsheet works if it records the date each letter arrived.