Every transaction of sale is required to be reported as taxable income or loss on your tax return.  Cryptocurrency trades are not eligible for like-kind exchanges. 

Every sale is considered first in first out method unless you specifically state which bitcoin purchase is sold based on purchase date.

The procedure will remain the same for 2018 unless new legislation would apply.  Currently there is no information about changes for this procedure.

No, the money does not have to leave the exchange before it's a taxable event.  It would be like buying stock, selling it and leaving the money in your account such as Charles Schwab; or reinvesting dividends.  This is taxable income regardless if you take the money or leave it sitting there or reinvest it.

For more information on bitcoin transactions review below.

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