SEC Form 6-K filed by Banco Santander S.A. Sponsored ADR (Spain)

FORM 6-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Report of Foreign Issuer

Pursuant to Rule 13a-16 or 15d-16 of

the Securities Exchange Act of 1934

For the month of July, 2025

Commission File Number: 001-12518

Banco Santander, S.A.

(Exact name of registrant as specified in its charter)

Ciudad Grupo Santander

28660 Boadilla del Monte (Madrid) Spain

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

Banco Santander, S.A.

TABLE OF CONTENTS

Item 1

¹ Closing Price of the Bank’s share on 28 July 2025.

Non-IFRS and alternative performance measures

This document contains financial information prepared according to International Financial Reporting Standards (IFRS) and taken from our consolidated financial statements, as well as alternative performance measures (APMs) as defined in the Guidelines on Alternative Performance Measures issued by the European Securities and Markets Authority (ESMA) on 5 October 2015, and other non-IFRS measures. The APMs and non-IFRS measures were calculated with information from Grupo Santander; however, they are neither defined or detailed in the applicable financial reporting framework nor audited or reviewed by our auditors. We use these APMs and non-IFRS measures when planning, monitoring and evaluating our performance. We consider them to be useful metrics for our management and investors to compare operating performance between periods. APMs we use are presented unless otherwise specified on a constant FX basis, which is computed by adjusting comparative period reported data for the effects of foreign currency translation differences, which distort period-on-period comparisons. Nonetheless, the APMs and non-IFRS measures are supplemental information; their purpose is not to substitute IFRS measures. Furthermore, companies in our industry and others may calculate or use APMs and non-IFRS measures differently, thus making them less useful for comparison purposes. For further details on APMs and Non-IFRS Measures, including their definition or a reconciliation between any applicable management indicators and the financial data presented in the consolidated financial statements prepared under IFRS, please see the 2024 Annual Report on Form 20-F filed with the U.S. Securities and Exchange Commission (the SEC) on 28 February 2025 (https://www.santander.com/content/dam/santander-com/es/documentos/informacion-sobre-resultados-semestrales-y-anuales-suministrada-a-la-sec/2025/sec-2024-annual
-20-f-2024-disponible-solo-en-ingles-es.pdf), as well as the section “Alternative performance measures” of this Banco Santander, S.A. (Santander) Q2 2025 Financial Report, published on 30 July 2025 (https://www.santander.com/en/shareholders-and-investors/financial-and-economic-information#quarterly-results). Underlying measures, which are included in this document, are non-IFRS measures.

The businesses included in each of our geographic segments and the accounting principles under which their results are presented here may differ from the businesses included and local applicable accounting principles of our public subsidiaries in such geographies. Accordingly, the results of operations and trends shown for our geographic segments may differ materially from those of such subsidiaries.

Forward-looking statements

Santander hereby warns that this document may contain 'forward-looking statements', as defined by the US Private Securities Litigation Reform Act of 1995. Such statements can be understood through words and expressions like 'expect', 'project', 'anticipate', 'should', 'intend', 'probability', 'risk', 'VaR', 'RoRAC', 'RoRWA', 'TNAV', 'target', 'goal', 'objective', 'estimate', 'future', 'ambition', 'aspiration', 'commitment', 'commit', 'focus', 'pledge' and similar expressions. They include (but are not limited to) statements on future business development, shareholder remuneration policy and NFI. However, risks, uncertainties and other important factors may lead to developments and results that differ materially from those anticipated, expected, projected or assumed in forward-looking statements. The important factors below (and others mentioned in this document), as well as other unknown or unpredictable factors, could affect our future

development and results and could lead to outcomes materially different from what our forward-looking statements anticipate, expect, project or assume:

• general economic or industry conditions (e.g., an economic downturn; higher volatility in the capital markets; inflation; deflation; changes in demographics, consumer spending, investment or saving habits; and the effects of the wars in Ukraine and the Middle East or the outbreak of public health emergencies in the global economy) in areas where we have significant operations or investments;

• exposure to market risks (e.g., risks from interest rates, foreign exchange rates, equity prices and new benchmark indices);

• potential losses from early loan repayment, collateral depreciation or counterparty risk;

• political instability in Spain, the UK, other European countries, Latin America and the US;

• changes in monetary, fiscal and immigration policies and trade tensions, including the imposition of tariffs and retaliatory responses;

• legislative, regulatory or tax changes (including regulatory capital and liquidity requirements) and greater regulation prompted by financial crises;

• acquisitions, integrations, divestitures and challenges arising from deviating management’s resources and attention from other strategic opportunities and operational matters;

• climate-related conditions, regulations, targets and weather events;

• uncertainty over the scope of actions that may be required by us, governments and other to achieve goals relating to climate, environmental and social matters, as well as the evolving nature of underlying science and potential conflicts and inconsistencies among governmental standards and regulations. Important factors affecting sustainability information may materially differ from those applicable to financial information. Sustainability information is based on various materiality thresholds, estimates, assumptions, judgments and underlying data derived internally and from third parties. Sustainability information is thus subject to significant measurement uncertainties, may not be comparable to sustainability information of other companies or over time or across periods and its inclusion is not meant to imply that the information is fit for any particular purpose or that it is material to us under mandatory reporting standards. The sustainability information is for informational purposes only, without any liability being accepted in connection with it except where such liability cannot be limited under overriding provisions of applicable law;

• our own decisions and actions, including those affecting or changing our practices, operations, priorities, strategies, policies or procedures;

• changes affecting our access to liquidity and funding on acceptable terms, especially due to credit spread shifts or credit rating downgrade for the entire group or core subsidiaries;

• our exposure to operational losses; and

• potential losses associated with cyberattacks, data breaches, data losses and other security incidents.

Forward looking statements are based on current expectations and future estimates about Santander’s and third-parties’ operations and businesses and address matters that are uncertain to varying degrees, including, but not limited to developing standards that may change in the future; plans, projections, expectations, targets, objectives, strategies and goals relating to environmental, social, safety and governance performance, including expectations regarding future

execution of Santander’s and third parties’ energy and climate strategies, and the underlying assumptions and estimated impacts on Santander’s and third-parties’ businesses related thereto; Santander’s and third-parties’ approach, plans and expectations in relation to carbon use and targeted reductions of emissions; changes in operations or investments under existing or future environmental laws and regulations; and changes in government regulations and regulatory requirements, including those related to climate-related initiatives.

Forward-looking statements are aspirational, should be regarded as indicative, preliminary and for illustrative purposes only, speak only as of the date of this document and are informed by the knowledge, information and views available on such date and are subject to change without notice. Banco Santander is not required to update or revise any forward-looking statements, regardless of new information, future events or otherwise, except as required by applicable law.

Not a securities offer

This document and the information it contains does not constitute an offer to sell nor the solicitation of an offer to buy any securities.

Past performance does not indicate future outcomes

Statements about historical performance or growth rates must not be construed as suggesting that future performance, share price or results (including earnings per share) will necessarily be the same or higher than in a previous period. Nothing in this document should be taken as a profit and loss forecast.

SIGNATURE

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.