Under-reamed piles are bored cast in situ concrete piles having one or multiple bulbs formed by enlarging the diameter of the pile at the desired location. The position of the bulb in an under-reamed pile, along the length of the pile, significantly influences the uplift capacity of the pile. In this study, a numerical investigation is carried out in order to determine the optimal position of the bulb to achieve maximum uplift capacity of under-reamed piles subjected to undrained loading. The effect of the position of bulb in single and double under-reamed piles subjected to uplift loading in homogeneous clay is evaluated using the finite element (FE) method-based program PLAXIS 2D. The geometry of the under-reamed pile is in accordance with the standard guidelines, i.e., as per IS 2911–3 (1980). In the FE analysis, the undrained clay is modelled using Mohr–Coulomb model with an undrained option, i.e., \(\phi\)  = 0 and the pile is linear elastic. The present study results are presented as design charts by evaluating the uplift capacity of under-reamed piles with bulb/s positioned at different locations normalized with reference to maximum uplift capacity (based on the IS code guidelines). The failure mechanism is also evaluated and presented for single and double under-reamed piles. The present study results will provide insight into the design of under-reamed piles where the bulb is placed at different positions other than the prescribed location. Moreover, the study also provides insight into the optimum location of bulb for single and double under-reamed piles in clay.