QuickLinks -- Click here to rapidly navigate through this document

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 8-K/A

(Amendment No. 1)

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): April 28, 2005

SIMON PROPERTY GROUP, INC.
(Exact name of registrant as specified in its charter)

Delaware   001-14469   046268599
(State or other jurisdiction
of incorporation)		   (Commission
File Number)		   (IRS Employer
Identification No.)


115 WEST WASHINGTON STREET INDIANAPOLIS, INDIANA 46204
(Address of principal executive offices) (Zip Code)

Registrant's telephone number, including area code: 317.636.1600

Not Applicable
(Former name or former address, if changed since last report)

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:

o
Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o
Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o
Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o
Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

        Simon Property Group, Inc. (the "Registrant") hereby amends its Current Report on Form 8-K dated and filed with the Securities and Exchange Commission on April 28, 2005 to amend Exhibit 99.1, the Supplemental Information Package, which contained an erroneous table on page 16 of the exhibit. No other changes are being made to the exhibit or report.

Item 9.01. Financial Statements and Exhibits

        Financial Statements:

        Exhibits:

Exhibit No.
   Description
   Page Number in
This Filing
99.1   Supplemental Information as of March 31, 2005   4

2


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 thereunto duly authorized.

        Dated: April 29, 2005

    SIMON PROPERTY GROUP, INC.

 
 
By:
 
/s/ STEPHEN E. STERRETT
Stephen E. Sterrett,
Executive Vice President and
Chief Financial Officer

3

SIMON PROPERTY GROUP
Table of Contents
As of March 31, 2005

Description
    
   Page
Exhibit 99.1   Supplemental Information    
    Company Overview    
    Overview (reporting calendar, stock information, and corporate ratings)   5-6
    Ownership Structure   7
    Changes in Common Shares and Unit Ownership   8

 
 
Financial Data
 
 
    Selected Financial and Equity Information   9
    Unaudited Pro-Rata Statement of Operations   10-11
    Unaudited Pro-Rata Balance Sheet   12
    Reconciliation of NOI to Net Income   13
    Computation of Comparable Property NOI Growth   14
    Analysis of Other Income and Other Expense   15
    NOI Composition   16

 
 
Operational Data
 
 
    U.S. Portfolio GLA, Occupancy & Rent Data   17
    Regional Mall Operational Information   18
    Regional Mall Lease Expirations   19
    Regional Mall Top Tenants   20
    Regional Mall Anchor/Big Box Openings, 2005—2007   21
    Regional Mall Property Listing   22-26
    U.S. Premium Outlet® Centers Operational Information   27
    U.S. Premium Outlet® Centers Lease Expirations   28
    U.S. Premium Outlet® Centers Top Tenants   29
    U.S. Premium Outlet® Centers Property Listing   30
    Community/Lifestyle Centers Operational Information   31
    Community/Lifestyle Centers Lease Expirations   32
    Community/Lifestyle Centers Top Tenants   33
    Community/Lifestyle Centers Property Listing   34-35
    International Operational Information   36
    International Property Listing   37-39

 
 
Development Activity
 
 
    Capital Expenditures in the U.S. Portfolio   40
    U.S. Development Activity Report   41-44
    International Development Activity Report   45

 
 
Balance Sheet Information
 
 
    The Company's Share of Total Debt Amortization and Maturities by Year   46
    Summary of Indebtedness   47
    Summary of Indebtedness by Maturity   48-54
    Unencumbered Assets   55-58
    Preferred Stock/Units Outstanding   59



QuickLinks

SIGNATURES