X0508 4 2024-08-02 0001979330 NB Bancorp, Inc. NBBK 0001222378 CAMPANELLI JOSEPH P 1063 GREAT PLAIN AVE NEEDHAM MA 02492 1 1 1 President & CEO Chairman of the Board 0 Common Stock 2024-08-02 4 P 0 5000 17.4907 A 50000 D Common Stock 2024-08-05 4 P 0 3000 16.44 A 53000 D Common Stock 40000 I By 401(k) Common Stock 40000 I By IRA The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $17.49 to $17.51, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (1) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $16.40 to $16.48, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (2) to this Form 4. /s/ Steven Lanter, pursuant to power of attorney 2024-08-06