So, I was looking into the IRS rules for capital gains in the US. They say if you don’t know the purchase price, you just assume it was $0. But what if you know the purchase price, or cost basis, but have no clue about the sale price or the date? Here’s an example: I bought 0.01 BTC for $500 back in 2021, and I definitely sold it sometime that year, but I can’t remember when or for what amount. How would I go about figuring out the gain in this case?
Based on everything you presented, I'm guessing you were keeping it in a wallet that didn't belong to an exchange [regardless of its nature]... I believe you can still find the missing information [date and its price at the time of sale] by connecting the dots on an "explorer [look where the output of the first transaction was used as an input]".
If you don't know how much you sold it for, obviously, you won't be able to calculate it. I understand that you bought it in a CEX and probably sold it in a CEX as well? If so there will be a history at the CEX. Because if it was in a decentralized exchange I don't think you would be eating your head off to declare it, let alone such a small amount. How much would be the profit? $200? $500?
Give us more details, otherwise we will have to consult our crystall ball, as NotFuzzyWarm points out.
You are more specific about buy date that mean you know the platform or the place you made the purchase from, and thus you can get the Bitcoin address.
All bitcoin data is open source and can be traced by everyone so it will be easy to know the date, signature and selling price.
go to https://blockchair.com/pdf/statement:
Paste your Bitcoin/Altcoin addressSelect the reporting periodDownload your WALLET STATEMENT
He can still keep track of his trading history if he some through CEX or DEX.
All he has to do is to check his wallet history for the year the trading was executed if sold through DEX since he knows the quantity of the BTC.
A simple solution is to check your bank statements (assuming you used a bank account to receive the money) since it must be kept X year(s).
If you can access your account online, banks usually have a search function. The good thing is that as it happened in 2021, you wouldn't have to search much.
If you used cash, use any price that suits you lol, since they can't control it.
In the worst case, you estimate a period at which you have sold and compare it with the price by looking at coinmarketcap (I know it's a lazy and a bit risky method but that's what I would do as the last option). Otherwise you really need to find more history, from your wallet, your account on an exchange or whatever.
If you give us more information we can give you more directions to help
the usual pain with the taxes