If your employer reimburses you for your expenses using a per diem allowance, an employee can generally use the allowance as proof of expenses.incurred (for purposes of reporting adequately to the employer). However, for a 100% owner/employee this isn't the case. In a "related party" transaction,(such as this) the 100% owner/employee would have to substantiate ALL expenses incurred. There is no limit (per se); but the expenses must be "ordinary and necessary" and not 'lavish or extravagant".