The real-time robust and secure operation of power systems has become a challenging task, as the operating state evolves rapidly due to uncertainties associated with increasing renewable generation, less predictable loads, and various forms of contingencies. Therefore, an online voltage stability assessment is required to avoid any undesirable system behaviours or a large-scale blackout. Such evaluation is not just difficult but also computationally intensive mainly due to the continuously changing state of a grid. This study presents a numerically robust and fast algorithm for online voltage stability assessment with ease of implementation and programming. The proposed approach updates distance of voltage collapse in real-time by incorporating base-case collapse point solution and incoming data from measurement devices. Implementation of the proposed algorithm is described in detail, and its performance is validated on different IEEE test cases.