X0609 4 2026-03-19 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 2026-03-19 4 P 0 2500 20.16 A 396661 D Common Stock 47000 I By IRA Common Stock 49597 I By 401(k) Common Stock 3677 I By ESOP Common Stock 3000 I As trustee for trust Includes shares of restricted stock which vest at a rate of 20% per year commencing on April 24, 2026. Includes shares of restricted stock which vest at a rate of 33 1/3% per year commencing on February 25, 2027. /s/ Steven T. Lanter, pursuant to Power of Attorney 2026-03-19