Caffeine Cutoff Calculator

The latest time you can drink coffee without wrecking tonight’s sleep.

Caffeine has a half-life of about 5-6 hours in most adults, meaning if you drink a coffee at 3 PM containing 100mg of caffeine, you still have 50mg in your system at 9 PM and 25mg at 2 AM. That residual caffeine does not prevent you from feeling sleepy, but it measurably reduces deep sleep even when you do not notice it. Studies have found that caffeine consumed 6 hours before bed reduced total sleep time by an hour. This calculator gives you a personalized cutoff time based on your intended bedtime, your sensitivity to caffeine, and the typical caffeine content of your usual drinks. Use it as a rule of thumb - genetic variation in caffeine metabolism is large. But for most people, following this cutoff time will meaningfully improve deep sleep quality and total sleep duration.

The Science

Caffeine’s half-life is 5-6 hours on average, with variation from 1.5 to 9.5 hours based on genetics (the CYP1A2 gene is the main metabolizer). A 2013 study in the Journal of Clinical Sleep Medicine found that 400mg of caffeine taken even 6 hours before bed significantly reduced total sleep time. The effect on deep sleep (slow-wave sleep) is particularly pronounced. This calculator uses the 8-hour cutoff recommended by most sleep researchers as a practical middle ground.

How It Works

1

Enter your intended bedtime.

2

Estimate your caffeine sensitivity (low, medium, high).

3

Note your typical caffeine source.

4

Get a cutoff time that works for tonight.

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When to Use This Calculator

Frequently Asked Questions

Caffeine’s effect on deep sleep is measurable even when you do not perceive it. You may fall asleep fine but get less restorative sleep throughout the night.
High sensitivity: noticeable buzz from small amounts, trouble sleeping even from afternoon coffee. Medium: can drink coffee midday but not late. Low: can drink coffee late and still sleep fine (rarer than people assume).
Yes, typically 2-15 mg per cup versus 80-100 mg for regular coffee. Usually not enough to affect sleep, but worth noting if you are very sensitive.
Dark chocolate contains 20-40 mg of caffeine per ounce. A late-night chocolate bar could affect sleep for sensitive people.
A crude test: drink a strong coffee and note when you feel the peak effect fade. If it is gone in 3 hours, you are a fast metabolizer; if it persists 6+ hours, you are slow.
Tea has about half the caffeine of coffee. Tea also contains L-theanine, which may slightly moderate caffeine effects. Still count it toward your cutoff.