Is there an (ideally online) credit card interest calculator that includes grace periods and lets you choose the interest calculation method (eg, "adjusted balance", "average daily balance", "two-cycle average daily balance", and the other methods listed at http://credit.about.com/od/creditcardbasics/tp/finance-charge-calculation.htm)?
Most online interest calculators are much simpler and don't compensate for the complexities of grace periods and interest calculation methods.