Company: MGRE
Filing Date: 2025-02-28
Form Type: S-3ASR
Source: 0001193125-25-042543
Chunk: 12

Company: AFFILIATED MANAGERS GROUP, INC.
Filing Date: 2025-02-28
Form: S-3ASR
Chunk 12
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 commence and the date on which the 
 subscription rights will expire;                                                                        |

| • |     | the extent to which the subscription rights may include an over-subscription privilege with respect to 
 unsubscribed securities; and                                                                           |

| • |     | if applicable, the material terms of any standby underwriting or purchase arrangement entered into by us in 
 connection with the offering of subscription rights.                                                        |

13

DESCRIPTION OF STOCK PURCHASE CONTRACTS AND STOCK PURCHASE UNITS AMG may issue stock purchase contracts, including contracts obligating holders to purchase from or sell to AMG, and AMG to sell to or purchase from the holders, a specified or varying number of shares of common stock, shares of preferred stock, or depositary shares at a future date or dates. The consideration per share of common stock, share of preferred stock, or depositary share and the number of shares of each may be fixed at the time the stock purchase contracts are issued or may be determined by reference to a specific formula set forth in the stock purchase contracts. Stock purchase contracts may be issued separately or as part of units, often known as stock purchase units, consisting of a stock purchase contract and any combination of:

| • |     | debt securities, |

| • |     | U.S. Treasury securities, or |

| • |     | any other securities described in the applicable prospectus supplement, |

which may secure the holders’ obligations to purchase or to sell, as the case may be, the common stock, preferred stock, or depositary shares under the stock purchase contracts. The stock purchase contracts may require AMG to make periodic payments to the holders of the stock purchase units or vice versa, and these payments may be unsecured or prefunded on some basis. The stock purchase contracts may require holders to secure their obligations under those contracts in a specified manner. The applicable prospectus supplement will describe the terms of the stock purchase contracts and stock purchase units, including, if applicable, collateral or depositary arrangements. 14

PLAN OF DISTRIBUTION General The securities may be sold:

| • |     | to or through underwriting syndicates represented by managing underwriters; |

| • |     | to or through one or more underwriters without a syndicate; |

| • |     | through dealers or agents; |

| • |     | to investors directly in negotiated sales or in competitively bid transactions; |

| • |     | in “at the market offerings,” within the meaning of Rule 415(a)(4) of the Securities Act