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

September 21, 2015

(Date of Report (Date of Earliest Event Reported))

EXTRA SPACE STORAGE INC.

(Exact Name of Registrant as Specified in Its Charter)

2795 East Cottonwood Parkway, Suite 400

Salt Lake City, Utah 84121

(Address of Principal Executive Offices)

(801) 365-4600

(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 (see General Instruction A.2. below):

ITEM 1.01 ENTRY INTO A MATERIAL DEFINITIVE AGREEMENT

On September 21, 2015, Extra Space Storage LP (the “Operating Partnership”), the operating partnership subsidiary of Extra Space Storage Inc. (the “Company”), issued $500.0 million aggregate principal amount of its 3.125% Exchangeable Senior Notes due 2035 (the “Notes”). The terms of the Notes are governed by an indenture, dated September 21, 2015 (the “Indenture”), among the Operating Partnership, as issuer, the Company, as guarantor, and Wells Fargo Bank, National Association, as trustee. A copy of the Indenture, including the form of Note and Guarantee of the Company, the terms of which are incorporated herein by reference, is attached as Exhibit 4.1 to this report. See Item 2.03 below for additional information.

The Notes and the shares of common stock of the Company (“Common Stock”), if any, issuable in certain circumstances upon exchange of the Notes have not been registered under the Securities Act of 1933, as amended (the “Securities Act”). The Operating Partnership offered and sold the Notes to the initial purchasers of the Notes (the “Initial Purchasers”) in reliance on the exemption from registration provided by Section 4(a)(2) of the Securities Act. The Initial Purchasers then sold the Notes to qualified institutional buyers pursuant to the exemption from registration provided by Rule 144A under the Securities Act.

In connection with the issuance and sale of the Notes, the Operating Partnership and the Company also entered into a registration rights agreement with Citigroup Global Markets Inc. and Wells Fargo Securities, LLC, in their capacity as representatives of the Initial Purchasers, dated September 21, 2015 (the “Registration Rights Agreement”). A copy of the Registration Rights Agreement, the terms of which are incorporated herein by reference, is attached as Exhibit 10.1 to this report.

Pursuant to the Registration Rights Agreement, the Company has agreed that it will:

If the Company does not meet these deadlines then, subject to certain exceptions, liquidated damages will accrue on the Notes to be paid semi-annually in arrears at a rate per annum equal to 0.25% of the principal amount of Notes to and including the 90th day following such registration default and 0.50% of the principal amount thereafter, for the period during which the registration default is not cured.

ITEM 2.03 CREATION OF A DIRECT FINANCIAL OBLIGATION OR AN OBLIGATION UNDER AN OFF-BALANCE SHEET ARRANGEMENT OF A REGISTRANT

On September 21, 2015, the Operating Partnership issued $500.0 million aggregate principal amount of Notes. After deducting the Initial Purchaser’s commissions and estimated offering expenses, the Operating Partnership received approximately $489.7 million in net proceeds in connection with the issuance and sale of the Notes. The Notes are general unsecured senior obligations of the Operating Partnership and rank equally in right of payment with all other senior unsecured indebtedness of the Operating Partnership. Interest will accrue from September 21, 2015 and is payable semiannually in arrears on April 1 and October 1 of each year, beginning on April 1, 2016 until the maturity date of October 1, 2035. The Operating Partnership’s obligations under the Notes are fully and unconditionally guaranteed by the Company.

The Notes bear interest at 3.125% per annum and contain an exchange feature, which provides that the Notes may, under certain circumstances and during certain periods, be exchangeable at the option of holders for cash (up to the principal amount of the Notes) and, with respect to any excess exchange value, into cash, shares of Common Stock or a combination of cash and shares of Common Stock at an initial exchange rate of 10.4827 shares per $1,000 principal amount of Notes. At the initial exchange rate, the Notes are exchangeable for Common Stock at an exchange price of approximately $95.40 per share, representing an approximately 27.5% premium over the last reported sale price of the Common Stock on September 15, 2015, which was $74.82 per share. The Notes will be exchangeable only under the following circumstances:

The Operating Partnership may redeem the Notes at any time to preserve the Company’s status as a real estate investment trust. In addition, on or after October 5, 2020, the Operating Partnership may redeem the Notes for cash, in whole or in part, at 100% of the principal amount plus accrued and unpaid interest, upon at least 30 days’ but not more than 60 days’ prior written notice to holders of the Notes. In either case, the Operating Partnership may only redeem the Notes prior to July 1, 2035 if it elects to settle its exchange obligation in respect of any Notes exchanged in connection with any such redemption entirely in cash or an effective registration statement is available for the resale of shares of Common Stock, if any, issuable upon exchange of the Notes in connection with any such redemption.

The holders of the Notes have the right to require the Operating Partnership to repurchase the Notes for cash, in whole or in part, on each of October 1, 2020, October 1, 2025 and October 1, 2030 (unless the Operating Partnership has called the Notes for redemption), and upon the occurrence of a fundamental change, in each case, for a repurchase price equal to 100% of the principal amount of the Notes plus accrued and unpaid interest.

A “fundamental change” will be deemed to have occurred at the time that any of the following occurs:

Certain events are considered events of default, which may result in the accelerated maturity of the Notes, including:

ITEM 9.01 FINANCIAL STATEMENTS AND EXHIBITS

(d) Exhibits

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.

EXHIBIT INDEX