Caffeine Half-Life Calculator
Half-life ranges from two hours to twelve.
Half-life ranges from two hours to twelve. How much caffeine is still circulating now and at bedtime, from a dose, the hours since, and your own half-life.
Still in your system
100 mg
50% of 200 mg · 1 half-lives elapsed
Caffeine's half-life averages about five hours and ranges from two to twelve between individuals, driven mostly by the CYP1A2 enzyme. That range is why the same afternoon coffee ruins one person's sleep and leaves another unaffected, and it is why the half-life here is an input rather than a constant. A 200 mg coffee at 2pm still leaves around 50 mg circulating at 11pm for an average metaboliser. That is enough to reduce deep sleep measurably even where falling asleep still feels easy, which is the part people miss. Several things shift it substantially. Pregnancy and oral contraceptives roughly double the half-life; smoking roughly halves it. Regular use builds tolerance to the alertness effect faster than to the sleep disruption.
How the Caffeine Half-Life Calculator works
How much caffeine is still circulating now and at bedtime, from a dose, the hours since, and your own half-life. The half-life is an input because it varies between people by a factor of six.
Also known as: how much caffeine is left in my system · latest time to drink coffee · caffeine before bed calculator · how long does caffeine last
Where to go next
The Caffeine Half-Life question rarely arrives on its own. These are the ones that usually come with it:
- Blood Alcohol Calculator — Predicts an average. Never predicts you.
- Water Intake Calculator — Daily hydration target adjusted for exercise and climate.
- Step Count Calculator — The 10,000 target came from a 1960s advert.
- BMI Calculator — Body mass index with category and healthy weight range.
Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.
Frequently asked questions
How long does caffeine stay in your system?
The average half-life is about five hours, with a range from two to twelve. After five half-lives roughly 3% remains, so an average metaboliser needs around 25 hours to fully clear a dose.
Why is the half-life an input rather than a fixed number?
Because the CYP1A2 enzyme that clears caffeine varies enormously between people. That range is the whole reason an afternoon coffee ruins one person's sleep and leaves another unaffected.
What changes my half-life?
Pregnancy and oral contraceptives roughly double it. Smoking roughly halves it. Some medications, including certain antibiotics and antidepressants, extend it substantially.
How late is too late for coffee?
Work backwards from your threshold. For an average metaboliser, a 200 mg coffee at 2pm leaves about 50 mg at 11pm — enough to reduce deep sleep measurably even if falling asleep still feels easy.
Does tolerance mean it stops affecting sleep?
Tolerance builds to the alertness effect faster than to the sleep disruption. Regular drinkers often stop feeling the lift while still losing sleep quality.
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