Absolute dating is the process of determining an approximate computed age in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty and precision. Absolute dating provides a computed numerical age in contrast with relative dating which provides only an order of events.

In archeology, absolute dating is usually based on the physical or chemical properties of the materials of artifacts, buildings, or other items that have been modified by humans. Absolute dates do not necessarily tell us precisely when a particular cultural event happened, but when taken as part of the overall archaeological record they are invaluable in constructing a more specific sequence of events.

In geology, absolute dating is usually based on physical or chemical properties of igneous rock formations which are closely associated with paleontological finds. Fossils are rarely dated directly.

Radiometric dating is based on the constant rate of decay of radioactive isotopes. Given an initial and a present quantity of such an isotope and its half-life, the time elapsed may be calculated. Various methods apply to different materials and timescales. If a very short period of time has passed, as measured in number of half-lives, a particular technique will be less accurate and more susceptible to statistical fluctuations in the inherently random decay events. If many half-lives of the isotope of interest have passed, too much of the sample may have decayed to provide an accurate reading.