The correct answer is B, One month ' s rent. Massachusetts General Laws Chapter 186, §15B limits an ordinary residential security deposit to no more than one month ' s rent.

A landlord may also generally collect first month ' s rent, last month ' s rent in advance, and the actual cost of purchasing and installing a lock and key, subject to applicable requirements. These permitted charges should not be confused with the security-deposit amount itself.

Massachusetts regulates security deposits unusually strictly. Failure to comply with segregation, receipt, accounting, interest, deduction, or return requirements can expose a landlord to significant liability.

Since August 1, 2025, Massachusetts also separately limits who may be required to pay residential broker fees: the party who actually hires the broker or salesperson bears that fee. A landlord cannot simply disguise an impermissible fee as an additional security payment.

Study Guide Reference: Property Management — Security Deposits and Residential Tenancies; M.G.L. c.186 §15B.