All major religions have a long history and have been here for centuries. The belief system has been in place for ages and there have been many generations who have followed them. On the other hand, a cult generally has a recent history and sometimes only has been around for a few years. There is no significant history involved and the belief system is often in the process of evolution.
All major religions have a following in millions, in certain cases, billions. People from all over the world follow them and believe in the set of principles that have been laid down in the Holy Scriptures. Contrary to this, cults have a small following often which is in hiding from the public. The people who follow them are passionate about their set of beliefs but often are in hundreds or not more than thousands.
The religions are acceptable to societies as well as governments and allowances are often made for the special occasions for all religions. Although people may not agree with each other, still they are able to understand that the other person follows a different set of beliefs and needs to be respected for that. In cults, there is little or no acceptability. Most people are unsure of the motives and smaller cults are often seen as a problem to society.
Religions have a clear pattern of leadership which has been established for centuries. Some religions have specified top leaders whereas others have learned men helping those who seek it. In case of cults, the leadership is generally a one man show. This person could be someone who truly believes in his or her convictions or does so for any other reason from which this person may benefit.