UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d)

of the Securities Exchange Act of 1934

Date ~~October~~of 30Report (Date of earliest event reported): November 7, 2025

Date of Report (Date of Earliest Event Reported)

Mallinckrodt plc

(Exact name of registrant as specified in its charter)

(Exact name of registrant as specified in its charter)


Ireland	001-35803	98-1088325
(State or other jurisdiction of incorporation)	(Commission File Number)	(IRS Employer Identification No.)

College Business & Technology Park, Cruiserath, ~~Blanchardstown, Dublin 15, Ireland~~

~~(Address of~~Blanchardstown, ~~principal~~Dublin ~~executive~~15, ~~offices) (Zip Code)~~Ireland

~~Registrant’s~~ ~~telephone~~(Address ~~number,~~of ~~including area~~principal ~~code:~~executive ~~+353 1 696 0000~~offices)

+353 1 696 0000

(Registrant's telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

¨☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ¨☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ¨☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ¨☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: None

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

¨	Emerging growth company
¨	If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.

Emerging growth company ☐

~~Item~~If ~~7.01~~an ~~Regulation~~emerging FDgrowth ~~Disclosure~~company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

OnItem ~~October 30, 2025, Mallinckrodt plc published the Information Statement attached hereto as Exhibit 99~~5.103 Amendments ~~and~~to ~~the~~Articles ~~Historical Financial Statements attached hereto as Exhibit 99.2, both~~ of ~~which~~Incorporation ~~are~~or ~~incorporated~~Bylaws; ~~herein~~Change byin ~~reference.~~Fiscal Year.

~~The~~On ~~information included in this Item~~ November 7~~.01~~, ~~Exhibit~~2025, ~~99.1~~Mallinckrodt ~~and~~plc ~~Exhibit~~(the ~~99.2 shall not be deemed~~ “~~filed~~Company”) ~~for~~determined ~~purposes~~to ofchange ~~Section~~the 18Company’s offiscal ~~the Securities~~year ~~Exchange~~end ~~Act~~from ofa ~~1934,~~52-53 asweek ~~amended~~year ~~(“Exchange~~ending ~~Act”)~~on ~~nor~~the ~~shall~~last itFriday beof ~~deemed~~December ~~incorporated~~to bya ~~reference~~calendar inyear ~~any~~ending ~~filing under~~on ~~the~~December ~~Securities~~31. ~~Act~~The ofCompany ~~1933,~~will asmake ~~amended,~~the orfiscal ~~the~~year ~~Exchange~~change ~~Act,~~on ~~except~~a asprospective ~~shall~~basis beand ~~expressly~~will ~~set~~not ~~forth~~adjust byoperating ~~specific~~results ~~reference~~for inprior ~~such filing~~periods.

~~Item~~Because ~~9.01~~the ~~Financial~~Company’s ~~Statements~~fiscal year end is changing by only five days, and ~~Exhibits~~the new fiscal year will commence with the end of the old fiscal year, the change is not deemed a change in fiscal year for purposes of reporting subject to Rule 13a-10 or 15d-10 of the Securities Exchange Act of 1934, as amended. Accordingly, the Company will not be required to file a transition report.

~~(d)~~The ~~Exhibits~~reporting periods and applicable Securities and Exchange Commission reports for the remainder of fiscal year 2025 and fiscal year 2026 are expected to be as follows:

Exhibit Number

Description

Fiscal Period

Reporting Period

Report To Be Filed

99.1

Information Statement, dated October 30, 2025

Fiscal year 2025

December 28, 2024 to December 31, 2025

Annual Report on Form 10-K

99.2

Historical Financial Statements

First quarter of fiscal 2026

January 1, 2026 to March 31, 2026

Quarterly Report on Form 10-Q

104

Cover Page Interactive Data File (embedded within the Inline XBRL document)

Second quarter of fiscal 2026

April 1, 2026 to June 30, 2026

Quarterly Report on Form 10-Q

Third quarter of fiscal 2026

July 1, 2026 to September 30, 2026

Quarterly Report on Form 10-Q

Fiscal year 2026

January 1, 2026 to December 31, 2026

Annual Report on Form 10-K

~~-2-~~Financial Reporting Impact

The number of operating days in the quarterly periods in fiscal year 2026 under a calendar year end will change as compared to the 52-53 weeks periods in fiscal year 2025 and prior periods, which will have an impact on the Company’s quarterly financial results as well as the comparative presentation of period over period information. The change in the Company’s fiscal year end to a calendar year end results in five additional operating days in the fiscal year 2025 and two additional operating days in the fiscal year 2026.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

~~MALLINCKRODT PLC~~

MALLINCKRODT PLC

Date: October 30, 2025

By:

/s/ Mark Tyndall

(registrant)

Name:

Mark Tyndall

Date:

November 7, 2025

By:

/s/ Christiana Stamoulis

Title:

Executive Vice President and Chief Legal Officer & Corporate Secretary

Christiana StamoulisPresident and Chief Financial Officer(Principal Financial Officer)

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