761 CMR, § 21.43
Stable monthly income is Borrower's gross monthly income from primary employment base earnings plus recognizable secondary income including a reasonable portion of anticipated or actual rental income from multi-unit structures being purchased or rehabilitated and other income as required to be recognized by law or prudent practice and custom of responsible Mortgage Lenders in Massachusetts. Secondary income of any Borrower, such as bonuses, commissions, overtime, or part-time employment, should only be recognized as "stable monthly income" if such items of secondary income are typical for the occupation, substantiated by Borrower's previous year's earnings, and continuation is probable based on foreseeable economic circumstances.
761 CMR, § 21.43