Major economies, including the United States and Britain, already tax cryptocurrency investment gains, though rates and allowances vary depending on holding periods, income levels and the nature of transactions.

In the United States, cryptocurrencies are treated as property. Profits from assets held for a year or less are taxed at ordinary federal income tax rates ranging from 10 to 37 percent, while gains on assets held longer qualify for federal long-term capital gains tax rates of 0, 15 or 20 percent, depending on income. State taxes and additional levies may apply.

Britain imposes capital gains tax at 18 or 24 percent, depending on income, with an annual tax-free capital…