497

MAINSTAY FUNDS TRUST

51 Madison Avenue

New York, NY 10010

December 26, 2012

Via EDGAR

Filing Desk

Securities and Exchange Commission

Office of Filings and Information Services

Branch of Registrations and Examinations

Mail Stop 0-25

100 F Street, NE

Washington, DC 20549

Re:	MainStay Funds Trust
	MainStay Balanced Fund
	File Nos. 333-160918 and 811-22321

Dear Sir or Madam:

On behalf of the registrant listed above and pursuant to Rule 497(c) under the Securities Act of 1933, as amended, attached for filing are exhibits containing interactive data format risk/return summary information that reflects the risk/return summary information in a supplement, dated December 17, 2012 to the Prospectus and Summary Prospectus for the MainStay Balanced Fund (Accession Number 0001144204-12-068230). The purpose of this filing is to submit an XBRL interactive data file in the manner provided by Rule 405 of Regulation S-T and General Instruction C.3.(g) of Form N-1A.

Any questions or comments on the filing should be directed to the undersigned at (973) 394-4436.

Sincerely,

/s/ Kevin M. Bopp

Kevin M. Bopp

Assistant Secretary

XML

MainStay Balanced Fund (Prospectus Summary): | MainStay Balanced Fund

MainStay Balanced Fund  

THE MAINSTAY GROUP OF FUNDS

MainStay Balanced Fund

Supplement dated December 17, 2012 (“Supplement”) to the

Summary Prospectus and Prospectus, each dated May 25, 2012

This Supplement updates certain information contained in the Summary Prospectus and Prospectus for MainStay Balanced Fund (the “Fund”), a series of MainStay Funds Trust (“Trust”). You may obtain copies of the Fund’s Summary Prospectus, Prospectus and Statement of Additional Information free of charge, upon request, by calling toll-free 800-MAINSTAY (624-6782), or by writing to NYLIFE Distributors LLC, Attn: MainStay Marketing Department, 169 Lackawanna Avenue, Parsippany, New Jersey 07054. These documents are also available on the Fund’s website at mainstayinvestments.com. Please review this important information carefully.

At a meeting held on December 10-12, 2012, the Trust’s Board of Trustees, including the Independent Trustees, approved the following changes, effective February 28, 2013:

Principal Investment Strategy Change  

The last paragraph of the Equity Investment Process section of the Summary Prospectus and Prospectus is changed to read as follows:

The Fund seeks to construct a broadly diversified portfolio across countries, sectors and industries using quantitative analysis to identify undervalued and overvalued securities. Investments are selected using an objective, disciplined and broadly-applied process, while seeking to limit exposure to risk.

PLEASE RETAIN THIS SUPPLEMENT FOR YOUR FUTURE REFERENCE.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

May 25, 2012

MainStay Balanced Fund (Prospectus Summary): | MainStay Balanced Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

MainStay Balanced Fund  

Supplement Text

ck0001469192_SupplementTextBlock

THE MAINSTAY GROUP OF FUNDS

MainStay Balanced Fund

Supplement dated December 17, 2012 (“Supplement”) to the

Summary Prospectus and Prospectus, each dated May 25, 2012

This Supplement updates certain information contained in the Summary Prospectus and Prospectus for MainStay Balanced Fund (the “Fund”), a series of MainStay Funds Trust (“Trust”). You may obtain copies of the Fund’s Summary Prospectus, Prospectus and Statement of Additional Information free of charge, upon request, by calling toll-free 800-MAINSTAY (624-6782), or by writing to NYLIFE Distributors LLC, Attn: MainStay Marketing Department, 169 Lackawanna Avenue, Parsippany, New Jersey 07054. These documents are also available on the Fund’s website at mainstayinvestments.com. Please review this important information carefully.

At a meeting held on December 10-12, 2012, the Trust’s Board of Trustees, including the Independent Trustees, approved the following changes, effective February 28, 2013:

Investment Strategy, Heading

rr_StrategyHeading

Principal Investment Strategy Change  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

The last paragraph of the Equity Investment Process section of the Summary Prospectus and Prospectus is changed to read as follows:

The Fund seeks to construct a broadly diversified portfolio across countries, sectors and industries using quantitative analysis to identify undervalued and overvalued securities. Investments are selected using an objective, disciplined and broadly-applied process, while seeking to limit exposure to risk.

Supplement Closing

ck0001469192_SupplementClosingTextBlock

PLEASE RETAIN THIS SUPPLEMENT FOR YOUR FUTURE REFERENCE.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	Other
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 17, 2012
Registrant Name	dei_EntityRegistrantName	MAINSTAY FUNDS TRUST
Central Index Key	dei_EntityCentralIndexKey	0001469192
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Dec. 17, 2012
Document Effective Date	dei_DocumentEffectiveDate	Dec. 17, 2012
Prospectus Date	rr_ProspectusDate	May 25, 2012