Australia: the greater of 2% or a flat amount, and the warning on your statement
Australian issuers set the minimum at the greater of 2% to 2.5% of the closing balance or a flat amount of about $20. The month's interest is taken from within that percentage, not added to it, so on a card at 20% a 2% minimum puts only about 0.33% of the balance towards the debt in the first month. That is the mechanism behind the very long payoff times the calculator reports here.
The closing balance matters too. The percentage is struck on the balance at the end of the statement period, so a purchase made the day before the statement closes raises next month's minimum, while the same purchase a day later does not.
Australia is unusual in requiring the arithmetic to be printed. Where the balance would take more than two years to clear, the National Credit Code obliges the statement to carry a minimum repayment warning: how long the balance would take to clear on minimum payments alone, what you would have to pay instead to clear it within two years, and the interest that faster plan would save. Those boxes routinely quote payoff figures in the decades, which is the same calculation this tool performs and a good check on the numbers above.
There is no statutory cap on Australian credit-card rates.