[Koha] Koha Circulation loan days is not calculating properly.

Dear All, I have defined Circulation and fine rules for my library. Here I have defined 7 loan days for students. But when the circulation time, it is calculating for 8 days suddenly. It was working very well in the beginning but suddenly from last two days it is showing 8 days. I couldn't understand the problem here. Please anyone can suggest me what should I do? Kind Regards, Ashok Francis Librarian New Delhi