Biological clock may refer to:
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Age and female fertility, decrease of female fertility with advancing maternal age
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Ageing, biological program that limits the lifespan of an individual
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Biological rhythms
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Internal clock, the timeframe sensed by the individual's body which is largely affected by the light-dark cycle
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Circadian clock, a molecular mechanism that results in a circadian rhythm in a living organism
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Circadian rhythm, biological process that displays an oscillation about 24 hours, such as the human sleep-wake cycle (the "body clock")
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Epigenetic clock, a set of DNA sites whose methylation levels can be used to measure aging throughout the body
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Molecular clock, a technique that uses the mutation rate of a biomolecule to deduce the time in prehistory when two life forms diverged
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Vernalisation, the induction of flowering by prolonged exposure to low temperatures, as during the winter in a temperate climate
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Menstrual cycle, the regular natural change that occurs in the female reproductive system that makes pregnancy possible
