Caffeine Half-Life Calculator
How much of that afternoon coffee is still with you at bedtime.
Reading your result
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How it is calculated
A five-hour half-life means half of it is gone every five hours. A 150mg coffee at 3pm still leaves roughly 50mg at 11pm — about an espresso's worth, arriving with you at bedtime.
Falling asleep and sleeping well are separate questions. Tiredness will still put you under, but the proportion of deep sleep drops. That is how "coffee doesn't affect my sleep" can be true and costly at the same time.
Half-life varies from three to seven hours between people, shifted by genetics, smoking, pregnancy and medication. Pregnancy in particular extends it considerably.
Frequently asked questions
How much caffeine is in a coffee?
A 355ml brewed coffee is roughly 120–150mg. A single espresso is 60–80mg and green tea 30–50mg, with wide variation between shops.
When should I stop for the day?
Eight hours before bed is the common guidance — 3pm for an 11pm bedtime. Sensitive sleepers should move it earlier.
What is a safe daily amount?
Up to 400mg a day for most adults, dropping to 200mg in pregnancy — roughly three cups and one and a half.
Half-life varies widely, so this is an average-based estimate. Pregnancy, liver conditions and certain medications change it substantially. Persistent sleep problems are worth discussing with a clinician.