Helical coiled springs are used as an integral part of many mechanical systems. Helical spring is also used in several industrial applications like balancing, brakes, vehicles suspensions in order to satisfy required functions. It applies forces, store or absorb energy, provide the mechanical system with the flexibility and maintain a force or a pressure. A mechanical spring is defined as an elastic body which has the primary function to deflect or distort under load, and to return to its original shape when the load is removed. The main objective of this review paper is to analyze various types of methods, formulas and theories used for the calculation of different stresses in helical coil spring. Prediction of stress involved in helical coil spring is a very important aspect. This study mainly focuses on various types of factors that affect the strength of coil spring. Reasons for the failure of coil spring were also studied.