Companies must report their annual revenue in SAM.gov so that a three year average may be computed. But is that only on completion of a company's fiscal year end? What about companies with fiscal year ends that do not coincide with December 31st? Are such companies also required to report their estimated receipts on January 1st to be compliant, or can they just report in SAM.gov at the end their latest/current fiscal year? Lastly, do $ size standards apply until a company's fiscal year end, or are they redetermined on calendar year start regardless of the company's fiscal year?

Thank you!

Do you mean "annual receipts"? If so, the rules about the calculation of annual receipts (aka, total income or gross income) are in the Code of Federal Regulations, 13 CFR 121.104. I won't restate or summarize them. You can read them yourself.