Company: BCDRF
Filing Date: 2025-07-30
Form Type: 6-K
Source: 0000891478-25-000103
Chunk: 0

Company: Banco Santander, S.A.
Filing Date: 2025-07-30
Form: 6-K
Chunk 0
---
#### 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.
<div align='center'>(Exact name of registrant as specified in its charter)</div>

#### Ciudad Grupo Santander

#### 28660 Boadilla del Monte (Madrid) Spain
<div align='center'>(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:

Form 20-F ☒ Form 40-F ☐</div>

#### BANCO SANTANDER, S.A.
#### ________________________

### TABLE OF CONTENTS
| Item 1. January - June 2025 Financial Report |     | 1 |

| January - June |     | 2025 |

Index

| 3  |     | SIGNIFICANT EVENTS IN THEPERIOD                     |
| 4  |     | KEY CONSOLIDATED DATA                               |
| 6  |     | BUSINESS MODEL                                      |
| 7  |     | GROUP FINANCIAL INFORMATION                         |
| 7  |     | General background                                  |
| 8  |     | Highlights of the period                            |
| 10 |     | Income statement                                    |
| 17 |     | Balance sheet                                       |
| 20 |     | Solvency ratios                                     |
| 21 |     | Risk management                                     |
| 25 |     | The Santander share                                 |
| 27 |     | FINANCIAL INFORMATION BY SEGMENT                    |
| 45 |     | SUSTAINABILITY                                      |
| 46 |     | CORPORATE GOVERNANCE                                |
| 47 |     | APPENDIX                                            |
| 48 |     | Financial information                               |
| 76 |     | Alternativeperformancemeasures                      |
| 88 |     | Interim condensed consolidated financial statements |
| 91 |     | Glossary                                            |
| 92 |     | Important information                               |

This report was approved by the board of directors on 29 July 2025, following a favourable report from the audit committee. Important information regarding this report