Generally, an expense is deductible if (1) it is related to a trade or business, (2) it is ordinary and necessary, and (3) it is paid or incurred in carrying on a trade or business.
First, for an expense to be related to a trade or business, your activities must rise to the level of a trade or business and there must exist a connection between the activities and the expense. For your activities to constitute a trade or business, you must enter into the activity for the purpose of making a profit, and your activities must be substantial and sustained.
Second, the expense must be an ordinary and necessary expense. An expense is ordinary if it is normal, usual or customary in the type of business in which it is incurred. An expense is necessary if it is appropriate or helpful to the business. In addition, the expense must be reasonable.
Third, the expense must be incurred in carrying on a trade or business. An individual is carrying on a trade or business only if he is actively engaged in the trade or business. Consequently, expenses relating to looking for a new trade or business, preparing for a new trade or business, or investigating the potential success of a new business are not deductible as business expenses. Such expenses must be capitalized, though an election can be made to amortize them over a five year period.
Certain trade or business expenses are not deductible even if they satisfy these tests. For example, expenses which violate public policy, such as bribes, are not deductible. In addition, expenditures for capital assets are not deductible, though a depreciation, amortization, or depletion deduction may be allowed.
Some of the deduction rules are complex and require informed judgment to determine whether a particular expense is deductible.