In this paper, the results of a parametric study conducted on the local joint flexibility (LJF) of three-planar tubular T-joints are presented and discussed. A set of finite element (FE) analyses were carried out on 81 FE models subjected to two types of axial loading in order to study the effects of geometrical characteristics of three-planar T-joint on the LJF factor (f LJF). Generated FE models were verified against available experimental data and parametric equations. The f LJF values in three-planar and uniplanar T-joints were compared. Results showed that the multi-planarity effect on the LJF is considerable and consequently the application of the equations already available for uniplanar T-joints to calculate the f LJF in three-planar T-joints may result in highly over- or under-predicting results. To tackle this problem, FE results were used to develop a new parametric formula for the prediction of the f LJF in axially loaded three-planar T-joints.