Cliff's Notes version: It is impossible to give you a useful answer without knowing a whole lot more about the specifics. Consult a tax attorney, pay for the advice, and share all the relevant information.
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I'm not an IRS agent, but I deal with a lot of them, including during audits. For what it's worth:
Would an IRS audit be so invassive that it would reveal my hobby activity
Originally Posted by ANONONE
Almost certainly not. The audit focuses of verifying that claimed deductions were legitimate and that all appropriate income was included. All taxpayers have a lot of expenditures that are not deductible, but if you don't claim a deduction or a loss on the tax return, the IRS doesn't give a damn. Paid $30,000 this year to put in a pool? The IRS doesn't care. Spent $5,000 for a trip to Europe? The IRS won't ask. Theoretically, if you, say,
volunteered the information that you'd spent $20,000 this year to hire a hit man to kill your business partner, they'd likely pass the information along. But if you didn't deduct it, they wouldn't ask about it, and you don't have to worry.
Don't just dump all your records on the auditor's desk. Respond to specific questions and requests; they will likely not disclose your hobby activity.
But see next section.
(and the secret cottage industry I have crafted to hide play funds)
Originally Posted by ANONONE
It depends a lot on what you mean by "the secret cottage industry I have crafted to hide play funds." If you're talking about an off-the-books business that generates cash that you don't tell your family about
and don't report on your tax return, yeah, that is exactly the type of thing the IRS would want to know about. [*] In fact, the single largest component of the so-called "tax gap" -- the difference between what the IRS should received under the tax law as written and what they actually receive -- is almost certainly not agressive tax planning, fancy offshore tax shelters, multi-national corporations with hordes of expensive tax lawyers, or "the filthy rich." It's small, Mom-and-Pop cash-based businesses that just take some of that cash under the table and never report it. Yep, those are the most typical "tax cheats."
The IRS would like to catch those folks, but it's not at all easy. The overall effort required versus likely return is not cost-efficient. The individual taxpayer like that is avoiding taxes, but not a huge amount; they account for a large portion of the tax gap only because there are so damned many of them compared to, say, the number of multi-national corporations with assets of $1 billion or more.
If you
are selected for an audit, the IRS often just asks for substantiation of your deductions and then checks your income to, e.g., information returns from your employers, brokers, banks, etc. as to how much income you earned. If you run a business, they'll likely ask to review the business' accounting records. Definitely if you run a business, and maybe even if you purport to be a wage-earner only, they can and will get bank statements, brokerage account statements, etc. (possibly credit card statements as well, not to mention Ebay or PayPal) looking for deposits and making sure that all of them are "accounted for." If you have deposits of $150,000 shown in your bank accounts but report income of only $120,000, they'll require you to explain where the other $30,000 came from and they'll want documentation.
Saying it was a gift or loan from family members won't be enough. Essentially, they start with the presumption that any accretion to wealth (e.g., deposit to your bank account) = income and you'll have to prove it isn't. So, if your bank statements include unreported income, you'll wind up having to pay tax (and penalties and interest) on it. And the audit result itself will raise the visibility and may lead to questions from SO and family.
But since this is money you're trying to keep secret, I'm guessing that you may arrange to get it in cash and keep it somewhere you can draw from it without the SO knowing. (A separate bank account she doesn't know about will come out normally in the audit; if they're suspicious, they can issue summonses to banks to identify any accounts in your name.) If it truly is cash, and there is no indication of it because it never touches a bank account, they probably won't find it. Unless:
1) An informant reports you to the IRS.
2) You're skimming off the top from an otherwise reported business, and in auditing the latter they see, e.g., that the reported income is disproportionately low compared to purchases, inventory, etc.
3) Law enforcement is already looking at you for some other reasons.
Any of those (and probably a few others) will lead to suspicion. And when the IRS gets suspicious, they can dig pretty hard. E.g., have a safety deposit box where you stash the cash? The government can find that by a summons to the bank and demand access. Or in some cases, where the reported income is very low compared to what you spend (whether in cash or not), they can do a "lifestyle audit/reconstruction" where they examine what you spend (whether deductible or not) and infer unreported income based on that. So they would look at your house, the cars you drive, your clothing, etc. and ask a lot of prying questions. Realistically, such audits are almost always limited to special cases. (It's how they convicted Al Capone. You can get away with theft, extortion, and murder, but cheat the tax man and you're in big trouble.)
The likelihood of an audit -- other than of the large corporations, which are audited thoroughly every damned year -- is fairly small. The likelihood of a more invasive audit (either because they're suspicious or you get hit for one of the National Research Project audits) is even smaller.
If you are audited, whether they're likely to turn something up which would be a surprise to your SO or family depends a lot on the specific details of that "cottage industry." Trading on eBay? Easy to find. Day-trading? Easy to find. Under the table sales from a business you report on Schedule C (or a separate corporation)? If they become suspicious, easy to find. Asking for extra money back on a credit card purchase, for something that you don't deduct? Unlikely they'll even look or care. Withdrawals from the ATM that you don't mention to your SO? Unlikely they'll even look or care -- it's deposits into your bank accounts, rather than withdrawals, that they're concerned about.
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[*] If you are reporting that income on your tax return, but your SO isn't aware of it, the audit could create a problem. If you tell the IRS "I earned $30,000 from trading on eBay, for which there was no information return, but here is where I reported it on the return" . . . the IRS is happy. But if your SO wasn't aware you were doing that, and asks what happened to the money you earned, you still have a problem.