For the record the U.S broker and
IRS do not decide how much tax you owe in your home country to the taxman. Why should a U.S broker need to know the amount of capital gains taxes you would owe in your home country? In plain English the U.S has nothing to do with the tax system in your home country beyond adhering to any DTA...lol. It is on you to calculate how much you would owe according to your local tax laws and whether you can deduct any taxes already withheld etc etc

. Just because this information is not transmitted as part of FATCA does not stop taxman asking for it later from U.S once they know of the accounts existence.
So you plan to say nothing until if the taxman inquiries and then you pay any back taxes you may owe them. Sounds like a great plan and kind tax authority if that's all that's required to resolve the tax matter

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btw thank you for your answers. let me elaborate;
I've stated I live in a 3rd world country because the direct tax collection(income, capital gains,etc.) here sucks so most tax is collected indirectly via consumption taxes like VAT. Almost everyone shows their gains and income of their business lower or not show it at all to evade taxes, it is the way of life. But is harder in a
bank account because the government forces almost all financial institutions to withold taxes. But government never collects anything from you directly. Even in the case of employees, their company withold the tax and pay it to the government. And employees evade tax by getting employed with minumum wage while they get a higher amount unreported.
So when government collect taxes here from interest payments, banks withold the amount and give it to them. No one declares anything. for example no one ever declared their
bitcoin gains and banks never cared if the money is coming from a bitcoin exchange. and because bitcoin exchanges aren't regulated financial institutions they don't withold anything.
Therefore, if there is no direct automatic information coming from IRS to local tax autorities I can always evade taxes. But if IRS tells them this person have this much tax to pay or share my total profits, then I will have to declare it. But so far what I have heard US is very reluctant to share this type of info with other nations.
And from afar this might looks like a great place to live because of the possibility of
tax evasion, however indirect taxes are just ridiculous. I don't think anyone would wanna pay twice the price for an iphone. one for you and one for the state. and of course ridicilous amount of political unstability

another reason why I've moved my money offshore.
Well time will show what will happen. thanks again.