Income from an occasional act or transaction, absent proof of efforts to continue those acts or transactions on a regular basis, isn't income from self-employment subject to the SE tax. (Rev Rul 58-112, 1958-1 CB 323; Rev Rul 55431, 1955-2 CB 312; Rev Rul 55-258, 1955-1 CB 433)

Regularity of activity, frequency of transactions, and the production of income are key elements in determining whether an activity will be considered a trade or business for SE tax purposes.

Income from an occasional act or transaction, without proof of efforts to continue on a regular basis, may not be income from self-employment. In Langford, TC Memo 1988-300, an assistant professor who co-authored a textbook without any obligation to work on later revisions was found not to have trade or business income from the activity. Even though the professor did ultimately revise the book, she was not subject to SE tax.