Ex Post Facto Note for family loan

There is no such requirement that I'm aware of. If it was set up originally as a loan and they are just creating documentation to conform to the original agreement, I don't see any problem with it. You could even date the documentation "as of" the date it was actually done, as long as you don't back-date something official like a notarization.

What is an "informal loan"? You do not say whether you mean by "informal" that your client's father-in-law was the source of the funds in question and said to your client when he provided those funds that the transaction was a gift and not a loan but that they later would pretend that it is a loan if they later chose to do so or whether they actually did agree from the outset that the transaction was a loan, not a gift, which your client agreed to repay with also then agreed interest and was "informal" only in the sense that your client did then not give his father-in-law a note or I.O.U. or whether you know or have have reason to believe that the funds in the bank account did not come from the father-in-law at all. But whether or not memorialized in/by a note or other writing, either it was a loan or it was not a loan.

Maybe the document the father-in-law is now preparing reflects a past loan actually made. But, maybe, not. One cannot tell from what you so far say. And maybe your client told you or you otherwise have reason to believe that the father-in-law never made a loan, whether "informal" or not, on the terms and conditions of which your client and you recently discussed. Or, maybe, you do not know or have reason to believe and instead have no reason to doubt that the transaction was a loan on such terms. One cannot tell from what you so far say.

Because you also do not post facts that would inform why the IRS is conducting an audit - random and routine? arising from what the IRS believes correctly or not is some sort "red flag" relating to your client in particular? other? - one cannot reasonably infer one way or another solely from what you so far post how likely it is that the IRS probably will or will not be satisfied with or instead probably would make an adverse claim as against your client or maybe even you if the IRS auditor disbelieves the genuineness of the document the father-in-law is now preparing.

And lest you dismiss this related consideration as only an introductory and preliminary aside or perhaps what you might believe to be an entirely trivial quibble, your indulgence in Latinate slogans confuses matters since, if you insist on using Latin expressions, you appear to refer without you adequately explaining whether you do refer more to a contemplated (true/accurate? false/fraudulent?) "nunc pro tunc" attempt than to "ex post facto" contemplated behavior.

That is, "ex post facto" (loosely translated: from a thing done afterward or, more simply, after the fact) generally refers to a later decided effect to be given what is acknowledged to be an earlier done act so as also openly to acknowledge that the effect, not the act itself, shall retroactively be treated differently from the original effect but not in the sense of being an attempt to cover up or otherwise to conceal the significance originally of the act and its original effect whereas "nunc pro tunc" (loosely translated: now for then), although sometimes referred to as a retroactive "correction" that is retroactive, more generally signifies doing something in the present but with the intention that it be perceived or at least treated as if it was done in the past so as relatedly to achieve an effect that would not be available if the act was not deemed to have been done in the past.

Sometimes, depending on intent and on full context, backdating is innocuous and, often, backdating triggers a presumption of impropriety and, sometimes, backdating, if discovered and provable, invites the imposition of serious sanction perhaps including criminal prosecution and conviction and sentence.

It possibly may be that all you are trying to say by your past tense use of the word "borrowed" even if you refer in present tense terms to what the client's father-in-law "is now preparing" is that he will be giving your client some sort of document, maybe in letter or in affidavit or in memorandum form or maybe even a "now" dated note, which will say in substance, now, that the client at some therein identified time in the past borrowed $__ on whatever is also the earlier agreed terms and conditions including interest which your client then agreed to repay.

It also possibly may be that what you are trying to say is that your client told you or you that you otherwise have reason to know that he contemplates obtaining a backdated document by which he and the document drafter/signer will try falsely to make it appear that that document was drafted and dated and given to him at the earlier therein date stated instead of whatever is the date the father-in-law will complete now preparing it.

Your succinctly while also vaguely posted scenario prevents definitive analysis which of the above alternatives is closer to the facts. But what your posting does so far suggest is that assuming as you seem to do that one's search ought be limited only for IRS regulations on family loan requirements, etc., probably deflects possibly dangerously from whether you and your client ought be paying more attention to perhaps more basic IRS related requirements of law.

See, for instance, 26 U.S.C. § 6694 and 7407 (maybe in the latter connection, especially sub-para. (b)(1)(D) of 7407), and related IRS regulations, relating to tax preparer liability, or, perhaps to 18 U.S.C. §§ 371 and 1001, relating to conspiracy and to false statements given government agencies, or 26 U.S.C. § 7206(1) and (2), and related IRS regulations, the latter of which have been given what the courts refer to as a "broad sweep" so as to encompass most variation of willful assistance in preparing false income tax returns including by way of backdating notes or comparable documents (re. which see, for example, U.S. v. Shortt Accountancy Corp., 785 F.2d

Nothing above is meant to suggest in any way that you have done or that you plan to do anything unlawful. But it is to suggest that your posting requires more careful thought by you whether your focus may be too narrow.