The design and development of single phase multi-component high entropy alloy (HEA) using conventional hit and trial method is a challenging job due to the large number of experimental trials required to find the right alloy composition from possible combinations of various alloying elements in the multi-component system. Present investigation reports a novel CALculation of PHAse Diagram (CALPHAD) based approach, which can significantly reduce number of experimental trials in a very time effective manner to find single phase HEAs. Here, 1287 equiatomic five-component alloy systems were studied using both parametric and CALPHAD approaches to find single phase fcc and bcc HEAs. The parametric approach reduced the number of trials to 124 whereas; CALPHAD approach reduced the number of alloy compositions to 10. Further, the experimental investigation on the 10 alloy systems reveals that six of them form single phase HEAs. In addition, Thermo-Calc software was also used effectively to draw the isothermal pseudo ternary sections at 1000 K varying all constituents elements from 5 to 35 atomic percent for the CoCuFeMnNi alloy system. Experimental evidences confirmed that the isothermal pseudo ternary diagrams are very useful to design non equiatomic single phase as well as multiphase HEAs in the absence of phase diagram for the five component systems. Display omitted •CALPHAD is effectively used to develop a method to design single phase HEAs with minimum effort.•Only nine experimental trials produce five brand new single phase equiatomic HEAs.•Pseudo isothermal ternary diagram is drawn to design non-equiatomic HEAs.•Success rate in design of HEAs is 60%.