In fact, by starting the business together, you and your sister have formed an informal partnership.
It would be much easier for the partnership to report its income and expenses as a partnership on form 1065 then allocate to each of you your share of the profit/loss through the Schedules K-1, rather than each of you reporting half of income and of every expense on a Schedule C.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
