In order to have your “hobby” considered a business, you must be pursuing the activity with the intent of making a profit. If this is not the case, the activity will be subject to the IRS hobby loss rules, which provide that such losses are generally deductible only to the extent of income produced by the activity. Furthermore, hobby expenses (only to the extent of hobby income) are deductible as a miscellaneous itemized deduction and are subject to the two-percent-of-adjusted-gross-income floor.
Referencing a recent article in The Tax Adviser, the determination of whether or not your hobby can be classified as a business involves a number of considerations.
But to end on a positive note, an activity is generally presumed NOT to be a hobby if net profits result in any three of five consecutive tax years ending with the tax year in question.