Caffeine and sleep
How long does caffeine last?
Longer than the buzz. Caffeine stays in your system for hours after you stop feeling it, and how long depends on the drink, the time and your own body.
The short answer
Caffeine reaches its highest level in your blood within about an hour. After that, your body clears it by half every four to five hours on average. That is caffeine’s half-life. In healthy adults it ranges from about two to ten hours, so there is no single number that fits everyone.
In practice, with an average five-hour half-life, a 12oz coffee (about 145mg) at 3pm still leaves about 56mg in your system at 10pm. That is more than a can of Coke. It takes about a day to fall below 5mg.
Caffeine half-life calculator
Left at your bedtime
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- Peak
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- Half gone
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- Under 5mg
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Tap or hover the chart to read any moment.
What you had
How fast you clear caffeine
Track a whole day in the free tracker
How long does coffee stay in your system?
Bigger drinks take longer to clear, because every doubling of the dose adds one more half-life before it fades. These figures use SlumberBrew’s average five-hour half-life and typical serving sizes.
| Drink | Caffeine | Left after 5 hours | Left after 10 hours | Under 5mg after |
|---|---|---|---|---|
| Espresso, 1 shot | 64mg | 33mg | 16mg | about 18½ hours |
| Brewed coffee, 8oz | 96mg | 49mg | 24mg | about 21½ hours |
| Brewed coffee, 12oz | 145mg | 74mg | 37mg | about 24½ hours |
| Cold brew, 12oz | 205mg | 104mg | 52mg | about 27 hours |
| Black tea, 8oz | 47mg | 24mg | 12mg | about 16 hours |
| Red Bull, 250ml | 80mg | 41mg | 20mg | about 20 hours |
| Monster, 473ml | 160mg | 81mg | 41mg | about 25 hours |
| Coca-Cola, 12oz | 34mg | 17mg | 9mg | about 14 hours |
Each “after 5 hours” figure is a little over half the dose, because caffeine is still being absorbed for the first hour. Brewed coffee varies a lot from cup to cup, so treat these as a guide. See how much caffeine is in coffee.
How long until caffeine wears off?
Feeling the caffeine wear off is not the same as the caffeine being gone. The alert feeling usually fades within a few hours, but the caffeine is still in your system for hours after that. That is why a coffee that no longer seems to be doing anything can still make it harder to fall asleep or sleep deeply.
The useful question for sleep is not “has it worn off?” but “how much will be left when I go to bed?”
What caffeine half-life means
A half-life is a percentage, not a fixed amount. If 100mg is in your system and the half-life is four hours, about 50mg remains after four hours. Four hours later, about 25mg remains—not zero.
Your body clears caffeine molecule by molecule, at a rate that is roughly tied to how much caffeine is present. When there is more caffeine, more is cleared in an hour. As the amount gets smaller, the amount cleared gets smaller too. The result is a steady percentage drop: half of what is there, then half of what remains. It never reaches exactly zero on paper, but the remainder eventually becomes too small to matter.
Imagine a 200mg drink and a five-hour half-life, which is SlumberBrew’s starting setting:
| Time since the drink | Approximate amount left |
|---|---|
| 5 hours | 100mg |
| 10 hours | 50mg |
| 15 hours | 25mg |
This is a simple example, not a promise about your body. Caffeine is absorbed over time rather than appearing in your bloodstream as a finished number the moment you finish a drink. SlumberBrew includes that short rise as well as the later clearance.
Why it varies
Caffeine clearance depends on your biology and can change with pregnancy, some medicines, smoking, age, and liver health. That is why a late coffee can be unnoticeable for one person and still affect another person’s night.
What it can mean for sleep
The amount and the timing both matter. In a controlled study, 400mg taken at bedtime, three hours before bed, or six hours before bed caused more sleep disturbance than a placebo. The six-hour dose was substantial, so this study supports taking dose and timing seriously; it does not create a universal bedtime rule. Read the study. For how dose and timing fit together, see how much caffeine you should have.
More than one drink
The calculator above follows a single drink. Real days stack up: a morning coffee is still partly there when the afternoon one arrives. The free tracker adds every drink you log into one curve and shows what may be left at bedtime. The cutoff calculator works backwards and gives the latest time for your next one.
See what may be left at bedtime
Common questions
How long until caffeine is completely gone?
There is no useful single answer. The amount keeps falling by halves, so a small remainder can last well after the noticeable effect has gone. SlumberBrew treats very small amounts as negligible rather than pretending its long tail is precise.
Does feeling tired mean the caffeine has worn off?
No. Feeling alert and clearing caffeine are related, but they are not the same measurement. The calculator and tracker estimate the amount remaining, not how awake you feel.
Does a stronger coffee last longer?
The half-life stays the same, but a bigger dose takes longer to fall to a trace. Doubling the caffeine adds one extra half-life, so a double espresso takes about five hours longer to clear than a single at an average half-life.
Can SlumberBrew measure my half-life?
No. It gives you an adjustable estimate. Sleep is affected by many things, so the tracker does not pretend to learn your metabolism from a few nights.
Sources
- European Food Safety Authority: Caffeine — typical half-life, absorption, variation, and intake guidance.
- Blanchard and Sawers (1983) — half-lives from 2.27 to 9.87 hours in the study group.
- Drake et al. (2013) — the effect of 400mg taken at different times before bed.
How much caffeine is in coffee? · How much caffeine should you have? · Use the caffeine cutoff calculator · Caffeine and sleep