Company: OSBC
Filing Date: 2025-05-08
Form Type: 424B3
Source: 0001104659-25-046065
Chunk: 99

Company: OLD SECOND BANCORP INC
Filing Date: 2025-05-08
Form: 424B3
Chunk 99
---
 the combined company until otherwise duly amended or repealed.

#### Closing and Effective Time of the Merger
The merger will be completed only if all conditions to the merger discussed in this proxy statement/ prospectus and set forth in the merger agreement are either satisfied or waived (subject to applicable law). Please see the section entitled “— Conditions to Complete the Merger” below.

The merger will become effective as of the date and time specified in the certificate of merger as duly filed with the Secretary of State of Delaware. The bank merger will become effective immediately following the merger.

In the merger agreement, we have agreed to cause the effective time to occur no later than (i) five business days after the satisfaction or waiver (subject to applicable law) of the last of the conditions in the merger agreement to occur, (ii) if elected by Old Second, the first calendar day of the calendar month following the calendar month in which the satisfaction or waiver (subject to applicable law) of the last of the conditions specified in the merger agreement to occur, or (iii) on another mutually agreed date. It currently is anticipated that the effective time will occur in the third quarter of 2025, subject to the receipt of regulatory approvals and waivers and other customary closing conditions, but we cannot guarantee when or if the mergers will be completed.

As described below, if the merger has not closed by December 31, 2025 (or March 31, 2026, if the only outstanding closing condition on December 31, 2025, is the receipt of all required regulatory approvals), the merger agreement may be terminated by either Old Second or Bancorp Financial, as long as the failure of the effective time to occur on or before that date is not caused by any breach of the merger agreement by the party electing to terminate the merger agreement.

### Conversion of Shares; Exchange Procedures
The conversion of Bancorp Financial common stock into the right to receive the merger consideration will occur automatically at the effective time of the merger.

#### Exchange Agent
Old Second will appoint an exchange agent for the purpose of exchanging shares of Bancorp Financial common stock for the merger consideration, pursuant to an exchange agent agreement entered into between Old Second and the exchange agent.

<div align='center'>63</div>

TABLE OF CONTENTS

### Exchange Procedures
As soon as reasonably practicable after the effective time, but in no event more than five business days after the effective time, Old Second will cause the exchange agent to mail transmittal materials to holders of record of Bancorp