Caffeine Window Calculator (Half-life Timing)
Enter when you had caffeine, the dose in mg, its half-life (4/5/6 h) and your planned bedtime — the tool estimates the latest safe intake time so that less than 50% remains at bedtime, plus the estimated remaining % when you go to sleep.
For self-reference only — estimates vary by body and medication; not a medical diagnosis. If sleep problems persist, see a doctor.
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What is it
Caffeine is cleared gradually: after one half-life about 50% remains, after two, 25%, and so on. Drinking coffee too late means part of the dose still circulates at bedtime, which can shorten deep sleep and fragment the night. This tool shows the window that keeps intake well before bed.
Notes & fun facts
A 3 p.m. coffee feels harmless until bedtime rolls around and sleep still takes forever — half-life math makes the invisible tail of that dose visible.
Origin & history
In the early 19th century, scientists isolated caffeine from coffee beans, bringing this stimulant into everyday awareness. Modern sleep research later confirmed that caffeine takes several hours to clear by half, and that late intake delays falling asleep and disrupts deep sleep. "Cut caffeine after the afternoon" has therefore become a common sleep-hygiene tip; this tool's estimates are for personal reference only.
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