“How long ago did the individual die?” is one of the most essential questions to ask when human remains are found. The body goes through an inevitable, permanent, and progressive series of physical and chemical changes almost immediately after death. By limiting the investigation period and thereby assisting in the reduction of the number of suspects in homicide cases to estimate the time since death (TSD), forensic pathologists are primarily needed through a comprehensive understanding of the anticipated development of post-mortem modifications. The time between when a death occurs and when the body is discovered is known as the post-mortem interval, or TSD. It also offers important details for creating the chain of events leading up to death. This chapter focuses on the different conventional techniques for calculating the duration since death. Other methods that were utilised will also be discussed. Previous techniques relied on the body cooling down, rigour mortis, ocular changes, putrefaction, supravital reactions, and stomach contents. Due to the relative simplicity of these techniques, only an approximate time could be calculated.