Pilmer Donald 4

4 · OLD SECOND BANCORP INC · Filed Feb 24, 2026

Form 4

Period: 2026-02-17

EVP

Transactions

Award
Restricted Stock Units
[F1]
2026-02-17+11,292→ 50,010 total
Tax Payment
Restricted Stock Units
[F2]
2026-02-21$20.57/sh−1,818$37,396→ 44,754 total

Holdings

Footnotes (4)

[F1]Each restricted stock unit represents a contingent right to receive one share of common stock. The reporting person was granted 11,292 restricted stock units on the date of the grant, 5,646 of which are time-based restricted stock units that vest on the third anniversary of the grant date, and 5,646 of which are performance-based restricted stock units that may vest and convert to shares within a range from 0% to 175% of the underlying performance-based restricted stock units originally awarded, depending on our compensation committee approved performance metrics. Vested shares, if any, will be delivered to the reporting person in 3 to 5 business days from the date of vesting.
[F2]Represents shares withheld by the issuer to satisfy applicable tax withholding obligations in connection with the vesting of 5,256 previously reported time-based restricted stock units, the remaining shares of which were issued and added to the reporting person's common stock holdings.
[F3]These shares are held in Mr. Pilmer's name outright.
[F4]These shares are held in spouse's IRA for which Mr. Pilmer is listed as a beneficiary.

Signature

/s/ Shirley Cantrell, Attorney-in-Fact|2026-02-24

Documents

1 file