Buying, selling and receiving each attract different taxes. What applies where.
Share-related taxes divide broadly into three: tax on the transaction itself when selling, tax on the gain when there is a profit, and tax on dividends received. They are different in nature, so knowing only one leads to miscalculating the total burden. Transaction taxes can apply even where the trade made a loss.
Gain taxation generally applies to the sale amount minus the purchase amount and costs. Proving the acquisition price is what matters here. Where the date and price of purchase cannot be confirmed, the calculation can go against you. Buying the same stock in several tranches also brings rules about which lots are treated as sold, which changes the result.
Many systems net gains and losses within the same period, taxing what remains after offsetting a profit in one holding against a loss in another. The scope of offsetting and whether losses carry forward differ by system, so mixing domestic and foreign trading means checking both sets of rules.
For foreign shares, the exchange rates at purchase and sale enter the gain calculation. A gain or loss can arise from currency movement even with the share price unchanged. Dividends are also frequently taxed at source in the other country, and separate rules govern how that is treated when calculating at home.
Rates, allowances and filing obligations vary by country and year and change frequently. Applying an older article or another country's example is error-prone. This piece explains only the frame of which tax attaches at which stage. For large amounts or mixed domestic and foreign trading, checking with a tax professional costs less in the end.
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