Algor mortis (Latin: algor—coolness; mortis—death) is the reduction in body temperature following death. This is generally a steady decline until matching ambient temperature, although external factors can have a significant influence.

A measured rectal temperature can give some indication of the time of death. The Glaister equation, for example, is (98.4° F − rectal temperature)/1.5, giving hours elapsed since death.

Algor mortis is usually the first sign of death, beyond the obvious, and is then followed by rigor mortis. As decomposition occurs the internal body temperature tends to rise again.