Galaxy clusters are massive bound systems. Their virialized core extending to ~ 1-2 Mpc, accretes matter from the outer region that extends for ~ 5-10 Mpc. We use the radial velocity profile of galaxies drawn from IllustrisTNG clusters with M200>10^14 Msun and 0.01<=z<=1.04 to explore cluster growth. We locate distinct dynamical regions and estimate mass accretion rate (MAR). The MAR is correlated with cluster mass and redshift. The typical MAR ~ 10^4-10^5 Msun/yr. Dense spectroscopy of real clusters infall region will soon be a platform for applying and testing these model results.