Company: BCDRF
Filing Date: 2025-10-31
Form Type: 424B5
Source: 0001193125-25-260533
Chunk: 322

Company: Banco Santander, S.A.
Filing Date: 2025-10-31
Form: 424B5
Chunk 322
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 accounts” or 
 “Roth IRAs”;                                              |

| • |     | persons subject to special tax accounting rules under Section 451 of the Internal Revenue Code of 1986, as 
 amended (the “Code”);                                                                                      |

| • |     | persons who own or are deemed to own 10% or more of our equity by vote or value; or |

| • |     | persons holding debt securities, contingent convertible capital securities, Conversion Shares or ADSs in 
 connection with a trade or business conducted outside the United States.                                 |

If an entity or arrangement that is classified as a partnership for U.S. federal income tax purposes owns debt securities, contingent convertible capital securities, ADSs or Conversion Shares, the U.S. federal income tax treatment of a partner will generally depend on the status of the partner and the activities of the partnership. Partnerships owning debt securities, contingent convertible capital securities, ADSs or Conversion Shares and partners in such partnerships should consult their tax advisors as to the U.S. federal income tax consequences of owning and disposing of the debt securities, contingent convertible capital securities, ADSs or Conversion Shares in their particular circumstances. As used herein, a “U.S. Holder” is a person that for U.S. federal income tax purposes is a beneficial owner of debt securities, contingent convertible capital securities, ADSs or Conversion Shares, as applicable and:

| • |     | an individual who is a citizen or resident of the United States; |

| • |     | a corporation, or other entity taxable as a corporation, created or organized in or under the laws of the United 
 States, any state therein or the District of Columbia; or                                                        |

| • |     | an estate or trust the income of which is subject to U.S. federal income taxation regardless of its source. |

This summary is based on the Code, administrative pronouncements, judicial decisions, final, temporary and proposed Treasury regulations, and the income tax treaty between the United States and Spain (the “Treaty”), all as of the date hereof, any of which is subject to change, possibly with retroactive effect. Persons considering the purchase of debt securities or contingent convertible capital securities of any series should consult their tax advisors with regard to the application of the U.S. federal, state, local and non-U.S.tax 158

consequences of owning and disposing of the securities offered hereunder in their particular situations. The applicable prospectus supplement may include a discussion of additional or alternative
U.S. federal income