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.
I thought it was such a useful suggestion that I went ahead and created them. I'm sure you're not the only one who could derive some benefit from them, I know I will.
When I have some additional time, I will add the option for grace-periods, but for now I wanted to get them up so you could use the calculations as-is from the article.
Enjoy.
(Disclosure: I'm the founder of the site they are hosted on and I wrote the code for the calculators)
If you want to ensure that you stop paying interest, the best thing to do is to not use the card for a full billing cycle.
Calculating credit card interest with precision ahead of time is difficult, as how you use the card both in terms of how much and when is critical.
