CALCULATOR

Caffeine Half-Life Calculator

How much caffeine is still in your system at bedtime, and the latest time you could have had it.

Caffeine remaining

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Still in your system at bedtime–

After 3 hours–

After 6 hours–

After 12 hours–

Your half-life–

Latest safe time for this dose–

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How long caffeine stays in your system

Caffeine has a half-life of roughly five to six hours in most adults, meaning half the dose is still circulating that long after you drank it. Take 200 mg at 3pm and around 100 mg remains at 9pm.

Individual variation is large and largely genetic, driven by the CYP1A2 enzyme. Fast metabolisers clear caffeine in around four hours and can drink coffee in the evening without issue. Slow metabolisers can take eight hours or more, and often do not realise caffeine is the reason their sleep is poor.

The threshold that matters is roughly 50 mg at bedtime. Above that, research finds measurable disruption to sleep architecture even in people who fall asleep without difficulty. You can sleep badly from caffeine without feeling wired.

Frequently asked questions

How long does caffeine stay in your system?

Half is cleared in about five to six hours for most adults, with the remainder taking considerably longer. Full clearance can take a day.

How much caffeine is left after 6 hours?

Roughly half of what you took, for an average metaboliser.

Why does caffeine affect me more than others?

Largely CYP1A2 genetics. Pregnancy, oral contraceptives and some medications also slow clearance.

Can caffeine affect sleep even if I fall asleep fine?

Yes. Studies find reduced deep sleep and altered architecture at doses that do not prevent sleep onset.

Sources

Institute of Medicine. Caffeine for the Sustainment of Mental Task Performance, pharmacokinetics chapter.
Drake C et al. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 2013.
Nehlig A. Interindividual differences in caffeine metabolism and factors driving caffeine consumption. Pharmacological Reviews, 2018.
EFSA Panel on Dietetic Products. Scientific Opinion on the safety of caffeine. EFSA Journal, 2015.
National Institutes of Health, Office of Dietary Supplements. Nutrient fact sheets. ods.od.nih.gov
NHS. Nutrition and health guidance. nhs.uk
US Departments of Agriculture and Health and Human Services. Dietary Guidelines for Americans, 2025-2030. dietaryguidelines.gov

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General information, not medical advice. Consult a qualified professional before changing your diet, especially with a medical condition.