https://www.ato.gov.au/General/Other-languages/In-detail/Inf...
But be careful! Actually read what your local tax office puts out. Assume nothing: it can be very easy to get yourself in to trouble.
For example:
- You buy BTC @ $1
- You exchange BTC @ $11 for $RANDOM
- You just made $10 :-) and you owe the taxman ~$3 (if you're in Australia)
- $RANDOM falls to ~$0
- So you didn't actually make a material profit
- But you still owe the taxman $3! (though you might be able to claim some sort of offset on your material loss of $RANDOM; IANAA)
- Now multiply all amounts by 10,000 and be sad
It's analogous to selling any asset. You buy gold, you sell gold at a profit and buy silver. You owe tax on the sale of the gold; you assume you'll pay this from the value you now hold in silver. The price of silver plummets. You still owe the tax on the sale of the gold.