Company: OSBC
Filing Date: 2025-06-30
Form Type: 11-K
Source: 0000357173-25-000063
Chunk: 3

Company: OLD SECOND BANCORP INC
Filing Date: 2025-06-30
Form: 11-K
Chunk 3
---
   7,754,859 | ​ |
| Administrative expenses                                       | ​ | ​                 |      27,480 | ​ |
| Total deductions                                              | ​ | ​                 |   7,782,339 | ​ |
| ​                                                             | ​ | ​                 |           ​ | ​ |
| Net increase                                                  | ​ | ​                 |  12,582,946 | ​ |
| Net assets available for benefits:                            | ​ | ​                 |           ​ | ​ |
| Beginning of year                                             | ​ | ​                 |  88,984,579 | ​ |
| End of year                                                   | ​ | $                 | 101,567,525 | ​ |
| ​                                                             | ​ | ​                 |           ​ | ​ |

The accompanying notes are an integral part of these financial statements.

6

<div align='center'>Old Second Bancorp, Inc. Employees’

401(k) Savings Plan and Trust</div>

### Notes to Financial Statements
<div align='center'>As of December 31, 2024 and 2023</div>

#### 1.Description of the Plan
The following is a brief description of the Old Second Bancorp, Inc. Employees’ 401(k) Savings Plan and Trust (the “Plan”). Participants should refer to the Plan document or the summary plan description for a more complete description of the Plan’s provisions.

#### General
The Plan is a defined-contribution plan established to provide deferred compensation benefits to eligible employees. Under the Plan, all nonunion employees of Old Second Bancorp, Inc. and certain of its affiliates (collectively, the “Company”) who have met certain eligibility requirements may elect to participate in the Plan. Union employees, leased employees, intermittent commissioned part-time employees and temporary employees as defined by the Employer’s Personnel Policy shall be excluded from participation in the Plan. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974, as amended (ERISA).

#### Contributions
Under provisions of the Plan, participants enter into agreements wherein each participant may elect to contribute an unlimited reduction in compensation to the Plan (subject to statutory wage deferral limitations). Maximum contribution limits of compensation may apply for certain highly compensated employees.

The Plan allows for a discretionary employer match contribution. The Plan has a “Safe Harbor” Plan provision, which allows a Company match equal to 100% of the first 3% of the participant’s eligible compensation contributed, and an additional Company match of 50% on the next 2%