According to Caffeine Informer, caffeine has a half-life that can range from 2.5 to 4.5 hours. Half-life is affected by various factors, including age, mental conditions and prescription drug use.
Caffeine Informer explains that the metabolization process begins as soon as caffeine is ingested, and all but 1 percent is absorbed within the first 45 minutes.
DotFit states that caffeine should not have any significant effect after its half-life, but trace amounts may remain in the body for up to one day. Individual differences in metabolic rate have a significant effect on how long you feel the effects of caffeine.