How long does caffeine last?
Caffeine’s half-life varies by person and circumstance. A five-hour half-life illustration means roughly half of a dose remains after five hours—not that its effects suddenly end then.
Individual differences matter: Pregnancy, medications, liver function, smoking and personal sensitivity can change caffeine metabolism. Ask a clinician about caffeine when health conditions or medicines are relevant.
How to find your actual cutoff
Use the same cutoff for one to two weeks while keeping bedtime fairly consistent. Notice sleep onset, awakenings and morning alertness. Move the cutoff earlier if sleep still feels affected.