50 Days is the Maximum. Don't go by that misleading campaign. Use your credit card only if you have to and kindly make all the payments in full atleast 3 days before the due date.
Using Credit Card for gaining points seems attractive. However, if you are careless and unable to pay the dues, then they will RIP you off 3 - 10 times than what they give. Points and offers come as you use and if you start accumulating too many, they will upgrade you to Platinum Card where there are no points :-)
