Securities Act of 1933 Registration No. 033-43529

Investment Company Act of 1940 Registration No. 811-06440

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 x

 oPre-Effective Amendment No.  ______

x Post-Effective Amendment No.  84

and

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940 x

 xAmendment No.  84

Fidelity Aberdeen Street Trust

 (Exact Name of Registrant as Specified in Charter)

245 Summer Street, Boston, Massachusetts 02210

(Address of Principal Executive Offices)(Zip Code)

Registrant’s Telephone Number: 617-563-7000

Marc Bryant, Secretary

245 Summer Street

Boston, Massachusetts 02210

(Name and Address of Agent for Service)

It is proposed that this filing will become effective on March 11, 2017 pursuant to paragraph (b) at 5:30 p.m. Eastern Time.

 xThis Post-Effective Amendment designates a new effective date for a previously filed post-effective amendment.

The purpose of this Post-Effective Amendment is to designate a new effective date, March 11, 2017, for the Post-Effective Amendment 81 previously filed on December 15, 2016, for Fidelity Freedom 2005 Fund Class K, Fidelity Freedom 2010 Fund Class K, Fidelity Freedom 2015 Fund Class K, Fidelity Freedom 2020 Fund Class K, Fidelity Freedom 2025 Fund Class K, Fidelity Freedom 2030 Fund Class K, Fidelity Freedom 2035 Fund Class K, Fidelity Freedom 2040 Fund Class K, Fidelity Freedom 2045 Fund Class K, Fidelity Freedom 2050 Fund Class K, Fidelity Freedom 2055 Fund Class K, Fidelity Freedom 2060 Fund Class K, and Fidelity Freedom Income Fund Class K.

The Post-Effective Amendment 82 filed on January 30, 2017 for Fidelity Advisor Freedom 2005 Fund Class Z6, Fidelity Advisor Freedom 2010 Fund Class Z6, Fidelity Advisor Freedom 2015 Fund Class Z6, Fidelity Advisor Freedom 2020 Fund Class Z6, Fidelity Advisor Freedom 2025 Fund Class Z6, Fidelity Advisor Freedom 2030 Fund Class Z6, Fidelity Advisor Freedom 2035 Fund Class Z6, Fidelity Advisor Freedom 2040 Fund Class Z6, Fidelity Advisor Freedom 2045 Fund Class Z6, Fidelity Advisor Freedom 2050 Fund Class Z6, Fidelity Advisor Freedom 2055 Fund Class Z6, Fidelity Advisor Freedom 2060 Fund Class Z6, Fidelity Advisor Freedom Income Fund Class Z6, Fidelity Freedom 2005 Fund Class K6, Fidelity Freedom 2010 Fund Class K6, Fidelity Freedom 2015 Fund Class K6, Fidelity Freedom 2020 Fund Class K6, Fidelity Freedom 2025 Fund Class K6, Fidelity Freedom 2030 Fund Class K6, Fidelity Freedom 2035 Fund Class K6, Fidelity Freedom 2040 Fund Class K6, Fidelity Freedom 2045 Fund Class K6, Fidelity Freedom 2050 Fund Class K6, Fidelity Freedom 2055 Fund Class K6, Fidelity Freedom 2060 Fund Class K6, and Fidelity Freedom Income Fund Class K6, which relates to a new prospectus for each of the Fidelity Freedom Funds and Fidelity Advisor Freedom Funds, is not affected by this request.

The Post-Effective Amendment 83 filed on February 3, 2017 for Fidelity Advisor Freedom 2005 Fund Class Transaction, Fidelity Advisor Freedom 2010 Fund Class Transaction, Fidelity Advisor Freedom 2015 Fund Class Transaction, Fidelity Advisor Freedom 2020 Fund Class Transaction, Fidelity Advisor Freedom 2025 Fund Class Transaction, Fidelity Advisor Freedom 2030 Fund Class Transaction, Fidelity Advisor Freedom 2035 Fund Class Transaction, Fidelity Advisor Freedom 2040 Fund Class Transaction, Fidelity Advisor Freedom 2045 Fund Class Transaction, Fidelity Advisor Freedom 2050 Fund Class Transaction, Fidelity Advisor Freedom 2055 Fund Class Transaction, Fidelity Advisor Freedom 2060 Fund Class Transaction, and Fidelity Advisor Freedom Income Fund Class Transaction, which relates to a new prospectus for Fidelity Advisor Freedom Funds, is not affected by this request.

The Prospectus and Statement of Additional Information (SAI) for Fidelity Freedom 2005 Fund Class K, Fidelity Freedom 2010 Fund Class K, Fidelity Freedom 2015 Fund Class K, Fidelity Freedom 2020 Fund Class K, Fidelity Freedom 2025 Fund Class K, Fidelity Freedom 2030 Fund Class K, Fidelity Freedom 2035 Fund Class K, Fidelity Freedom 2040 Fund Class K, Fidelity Freedom 2045 Fund Class K, Fidelity Freedom 2050 Fund Class K, Fidelity Freedom 2055 Fund Class K, Fidelity Freedom 2060 Fund Class K, and Fidelity Freedom Income Fund Class K are identical to those filed in Post-Effective Amendment No.81, the Part C is identical to the Part C filed in Post-Effective Amendment No. 83, and the Prospectus, SAI, and Part C are incorporated herein in their entirety by reference to those previously filed Post-Effective Amendments.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for the effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment No.84 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Boston, and Commonwealth of Massachusetts, on the 9th day of February 2017.

Fidelity Aberdeen Street Trust
By	/s/Stephanie J. Dorsey
	Stephanie J. Dorsey, President

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been

signed below by the following persons in the capacities and on the dates indicated.

(Signature)		(Title)	(Date)
/s/Stephanie J. Dorsey		President and Treasurer	February 9, 2017
Stephanie J. Dorsey		(Principal Executive Officer)
/s/Howard J. Galligan III		Chief Financial Officer	February 9, 2017
Howard J. Galligan III		(Principal Financial Officer)
/s/Abigail P. Johnson	†	Trustee	February 9, 2017
Abigail P. Johnson
/s/Elizabeth S. Acton	*	Trustee	February 9, 2017
Elizabeth S. Acton
/s/John Engler	*	Trustee	February 9, 2017
John Engler
/s/Albert R. Gamper, Jr.	*	Trustee	February 9, 2017
Albert R. Gamper, Jr.
/s/Robert F. Gartland	*	Trustee	February 9, 2017
Robert F. Gartland
/s/Arthur E. Johnson	*	Trustee	February 9, 2017
Arthur E. Johnson
/s/Michael E. Kenneally	*	Trustee	February 9, 2017
Michael E. Kenneally
/s/Marie L. Knowles	*	Trustee	February 9, 2017
Marie L. Knowles
/s/Mark A. Murray	*	Trustee	February 9, 2017
Mark A. Murray
/s/Jennifer Toolin McAuliffe	*	Trustee	February 9, 2017
Jennifer Toolin McAuliffe

†	By:	/s/Marc R. Bryant
		Marc R. Bryant, pursuant to a power of attorney dated December 16, 2015 and filed herewith.
*	By:	/s/Megan C. Johnson
		Megan C. Johnson, pursuant to a power of attorney dated January 1, 2017 and filed herewith.

POWER OF ATTORNEY

I, the undersigned Trustee of the following investment companies:

Fidelity Aberdeen Street Trust Fidelity Advisor Series II Fidelity Advisor Series IV Fidelity Boylston Street Trust Fidelity California Municipal Trust Fidelity California Municipal Trust II Fidelity Central Investment Portfolios II LLC Fidelity Charles Street Trust Fidelity Colchester Street Trust Fidelity Commonwealth Trust II Fidelity Court Street Trust Fidelity Court Street Trust II Fidelity Garrison Street Trust Fidelity Hereford Street Trust Fidelity Income Fund Fidelity Massachusetts Municipal Trust
Fidelity Merrimack Street Trust Fidelity Money Market Trust Fidelity Municipal Trust Fidelity Municipal Trust II Fidelity Newbury Street Trust Fidelity New York Municipal Trust Fidelity New York Municipal Trust II Fidelity Oxford Street Trust Fidelity Oxford Street Trust II Fidelity Phillips Street Trust Fidelity Revere Street Trust Fidelity Salem Street Trust Fidelity School Street Trust Fidelity Union Street Trust Fidelity Union Street Trust II Variable Insurance Products Fund V

in addition to any other Fidelity Fund for which the undersigned individual serves as Trustee (collectively, the “Funds”), hereby constitute and appoint Marc R. Bryant, my true and lawful attorney-in-fact, with full power of substitution, and with full power to sign for me and in my name in the appropriate capacity, all Registration Statements of the Funds on Form N-1A, or any successors thereto, any and all subsequent Amendments, Pre-Effective Amendments, or Post-Effective Amendments to said Registration Statements or any successors thereto, and any supplements or other instruments in connection therewith, and generally to do all such things in my name and behalf in connection therewith as said attorney-in-fact deems necessary or appropriate, to comply with the provisions of the Securities Act of 1933 and the Investment Company Act of 1940, and all related requirements of the Securities and Exchange Commission.  I hereby ratify and confirm all that said attorney-in-fact or his substitutes may do or cause to be done by virtue hereof.  This power of attorney is effective for all documents filed on or after December 16^th, 2015.

WITNESS my hand on this 16th day of December, 2015.

/s/Abigail P. Johnson

Abigail P. Johnson

POWER OF ATTORNEY

We, the undersigned Directors or Trustees, as the case may be, of the following investment companies:

Fidelity Aberdeen Street Trust Fidelity Advisor Series II Fidelity Advisor Series IV Fidelity Boylston Street Trust Fidelity California Municipal Trust Fidelity California Municipal Trust II Fidelity Central Investment Portfolios II LLC Fidelity Charles Street Trust Fidelity Colchester Street Trust Fidelity Commonwealth Trust II Fidelity Court Street Trust Fidelity Court Street Trust II Fidelity Garrison Street Trust Fidelity Hereford Street Trust Fidelity Income Fund Fidelity Massachusetts Municipal Trust Fidelity Merrimack Street Trust Fidelity Money Market Trust Fidelity Municipal Trust Fidelity Municipal Trust II Fidelity Newbury Street Trust Fidelity New York Municipal Trust Fidelity New York Municipal Trust II Fidelity Oxford Street Trust Fidelity Oxford Street Trust II Fidelity Phillips Street Trust Fidelity Revere Street Trust Fidelity Salem Street Trust Fidelity School Street Trust Fidelity Union Street Trust Fidelity Union Street Trust II Variable Insurance Products Fund V

in addition to any other Fidelity Fund for which the undersigned individuals serve as Directors or Trustees (collectively, the “Funds”), hereby revoke all previous powers of attorney we have given to sign and otherwise act in our names and behalf in matters involving any investment company for which FMR or an affiliate acts as investment adviser and hereby constitute and appoint Thomas C. Bogle, John V. O’Hanlon, Robert W. Helm, Megan C. Johnson, and Anthony H. Zacharski, each of them singly, our true and lawful attorneys-in-fact, with full power of substitution, and with full power to each of them, to sign for us and in our names in the appropriate capacities, all Registration Statements of the Funds on Form N-1A, or any successors thereto, any and all subsequent Amendments, Pre-Effective Amendments, or Post-Effective Amendments to said Registration Statements or any successors thereto, and any supplements or other instruments in connection therewith, and generally to do all such things in our names and behalf in connection therewith as said attorneys-in-fact deem necessary or appropriate, to comply with the provisions of the Securities Act of 1933 and the Investment Company Act of 1940, and all related requirements of the Securities and Exchange Commission.  We hereby ratify and confirm all that said attorneys-in-fact or their substitutes may do or cause to be done by virtue hereof.  This power of attorney is effective for all documents filed on or after January 1, 2017.

WITNESS our hands on this first day of January 2017.

/s/Elizabeth S. Acton	/s/Michael E. Kenneally
Elizabeth S. Acton	Michael E. Kenneally
/s/John Engler	/s/Marie L. Knowles
John Engler	Marie L. Knowles
/s/Albert R. Gamper, Jr.	/s/Jennifer Toolin McAuliffe
Albert R. Gamper, Jr.	Jennifer Toolin McAuliffe
/s/Robert F. Gartland	/s/Mark A. Murray
Robert F. Gartland	Mark A. Murray
/s/Arthur E. Johnson
Arthur E. Johnson