Is there a U.S. law that requires businessment while in the U.S. doing business to maintain a log of expenses?

Question

If yes, what is that law?

Answer 1

The law requires taxpayers, including business owners, to document the expenses they deduct on returns. IRS is particularly strict about a requirement that a log be kept for mileage deduction claims. Tax Court consistently rules 100% for IRS when this is not done.

Answer 2

No law that you have to keep a log of expenses. But if you don't have documentation on your expenses, you can't deduct them.