Md. Code, Tax - General § 10–401

In computing the adjustments under §§ 10-206 and 10-210 of this title, a nonresident shall allocate to the State income, losses, or adjustments derived in connection with a business that is carried on both in and out of the State and of which the nonresident is a partner, shareholder of an S corporation, or proprietor, or in connection with an occupation, profession, or trade carried on both in and out of the State by:

(1) separate accounting, if the Comptroller allows; or

(2) the method that the Comptroller requires to determine fairly the part of the income derived from or reasonably attributable to the trade, business, profession, or occupation carried on in the State.