Thyroid hormones have pervasive effects on growth and development in the fetus, child, and adolescent regulating calorigenesis and metabolic rate throughout the life.Â The study was made to investigate the levels of free triiodothyronine (fT3), free thyroxine (fT4) and thyroid stimulating hormone (TSH) of euthyroid subjects. The study included 713 male and 2633 female euthyroid subjects of RIMS, Jharkhand, India during December 2013 to November 2014. It has been found that free triiodothyronine level (p=0.000) varies remarkably among different age group and gender, free thyroxine level (p=0.999) remains almost unaltered throughout all decades of life and TSH level (p=0.000) decreases with age. The levels of free T3, free T4 and TSH have significant effects among gender with age. It is therefore concluded that there should be separate reference range among individuals so that the higher level of hormones in the early decades and the lower level in the older decade cannot be interpreted as abnormal results and under prediction and over prediction of results can be avoided.