Guide
How long does caffeine stay in your system
A plain guide to caffeine half-life, the variables that speed or slow clearance, and what it means for sleep timing.
The average half-life is around 5 hours
The half-life of caffeine — the time for your body to eliminate half of it — is typically 4–6 hours in adults. This means a 200mg dose at noon still leaves roughly 100mg at 5pm, 50mg at 10pm, and 25mg at 3am. The tail extends well past when you stop feeling the effect.
Sensitivity, medication, and biology shift the window
People with high caffeine sensitivity metabolise it more slowly, so the same dose lasts longer. Oral contraceptives and some medications can extend the half-life significantly. Pregnancy can roughly triple it. Smokers metabolise caffeine faster. The calculator uses a general sensitivity range — individual variation is real and significant.
The cutoff time is individual, not universal
The common advice to stop coffee by 2pm exists because of average half-life and average sleep times. If you are highly sensitive, sleep before 10pm, or drink large amounts, the cutoff needs to shift earlier. The Caffeine Half-Life Clock gives you a personalised estimate based on your intake and timing.