There is no U.S. filing-certification requirement
The United States has no equivalent of a mandatory certification that a tax professional must verify a sole proprietor's books above a revenue threshold. Nothing changes the filing procedure simply because receipts cross a line. What exists instead is selection for examination: returns are scored by a statistical model, the Discriminant Inventory Function or DIF score, that compares each return with others reporting similar income, and high-scoring returns are reviewed by a classifier.
Because the scoring formula is not published, this checker works the other way round. It applies widely used self-review rules of thumb to the figures most often questioned on a Schedule C: thin margins, outsized vehicle, meal, travel and home office deductions relative to receipts, repeated losses, and cash-intensive operations. Repeated losses matter for a separate reason: an activity that does not produce a profit in a set number of years within a five-year window can be challenged as a hobby rather than a business.
The thresholds shown are rules of thumb on a 2026 basis, not published IRS selection criteria, and you can enter your own income tier's audit rate from the IRS Data Book to compare. A flag does not mean a return is wrong; it means the deduction is one that gets looked at, so contemporaneous records matter most there.
This tool does not predict whether you will be audited and is not a substitute for professional review. Selection also depends on information-return matching, related examinations and random sampling. Discuss your return with a CPA or enrolled agent.
Frequently asked questions
Not by itself. What draws attention is a deduction that is large relative to receipts and without records. A properly documented, proportionate home office is an ordinary deduction.
Repeated losses can lead the IRS to question whether the activity is run for profit. Business plans, records and evidence of changes made to reach profitability are the usual response.