Although credit cards allow you to make interest-free purchases and earn rewards, they could pose a significant problem if the dues are not paid on time. Card companies give you options like “pay the minimum amount”, which can prove a major rip-off, especially for first-time users, if they forget the due date. Card companies usually offer an interest-free period of 45 to 55 days, but they may charge you around 3.5 per cent monthly interest after the due date.