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The short answer Caffeine peaks in your blood within about an hour and has a half-life of roughly 5 hours, so half of a morning coffee is still in you by early afternoon. You’ll usually feel it for 4 to 6 hours, but it keeps affecting sleep for longer. A 2023 meta-analysis suggests finishing coffee at least 8.8 hours before bed.
The number that matters for sleep is the half-life: how long your body takes to clear half of the caffeine you drank. The CDC’s travel health guidance puts it at approximately 5 hours for adults. Plug your own drinks into the calculator, or use the table below for a quick sense of the curve.
How much caffeine is left, hour by hour
This assumes a 200 mg coffee at 8 am (a large brewed cup can hold that much or more), a peak about an hour later, and a 5-hour half-life. It’s a simplified model; your own clearance may run faster or slower.
| Time | Hours after the peak | Caffeine left | Share of the dose |
|---|---|---|---|
| 9 am | 0 | About 200 mg | 100% |
| 2 pm | 5 | About 100 mg | 50% |
| 7 pm | 10 | About 50 mg | 25% |
| Midnight | 15 | About 25 mg | 12.5% |
| 5 am | 20 | About 12 mg | 6% |
| 10 am next day | 25 | About 6 mg | 3% |
Two things jump out. At 7 pm you still have roughly the caffeine of a can of cola on board. And a second cup at 2 pm doesn’t replace the first; it stacks on top of the 100 mg that’s still there.
How long until caffeine kicks in
Fast. MedlinePlus says caffeine reaches its peak level in your blood within one hour, and the CDC’s jet lag guidance notes it acts in about 20 minutes. That quick lift is why the afternoon coffee feels so harmless: by the time it fades, you’ve forgotten about it.
How long do the effects last?
MedlinePlus says you may feel the effects for four to six hours. Feeling it and being affected by it aren’t the same thing, though. Caffeine you no longer notice can still make sleep shallower and shorter.
The clearest evidence comes from a 2013 sleep study. Researchers gave adults 400 mg of caffeine at bedtime, 3 hours before bed or 6 hours before bed. Even the 6-hour dose reduced objectively measured sleep by more than an hour. The participants’ own sleep diaries showed a smaller loss that didn’t reach statistical significance, which is the uncomfortable part: you may not notice what caffeine is costing you.
How late can you drink coffee?
A 2023 meta-analysis pooled 24 studies and found caffeine cut total sleep by 45 minutes, added about 9 minutes to the time it took to fall asleep and trimmed deep sleep by about 11 minutes. To avoid losing sleep, the authors calculated that a cup of coffee (107 mg per 250 mL) should be drunk at least 8.8 hours before bedtime. A standard pre-workout supplement, at about 217 mg, needed at least 13.2 hours.
- Start from your bedtime. Not sure what it should be? The sleep calculator works backward from your wake-up time.
- Count back about 9 hours for regular coffee. An 11 pm bedtime means a roughly 2 pm cutoff; 10 pm means 1 pm.
- Count back further for big doses. Energy drinks, cold brew in large sizes and pre-workout powders often carry more caffeine than a standard cup. The meta-analysis put pre-workout at 13 hours.
- Move the cutoff earlier if you’re a slow clearer (see the factors below) or if you’ve been sleeping badly.
- Check the hidden sources. Tea, cola, chocolate and some pain relievers contain caffeine too.
Many sleep guidelines use a shorter rule. The 2013 study’s authors said its results support avoiding substantial caffeine for a minimum of 6 hours before bed, and the CDC’s jet lag advice says to stop 6 hours before bedtime. Six hours is the floor. If you’re struggling to sleep, the 8.8-hour figure is the better target.
Why caffeine lasts longer in some people
Five hours is an average, and people vary widely. Your liver does nearly all the work, mainly through an enzyme called CYP1A2, and a lot changes how fast that enzyme runs. A systematic analysis of 141 studies found:
- Smoking speeds clearance. Smokers clear caffeine faster, so their half-life is shorter.
- Oral contraceptives slow it down. The same analysis found they inhibit caffeine elimination, so it lingers longer.
- Liver disease slows it the most. In cirrhosis, the drop in clearance tracks how impaired the liver is.
Pregnancy has the biggest effect most people will ever experience. A 2021 review in BMJ Evidence-Based Medicine reports that caffeine’s half-life rises from about 5 hours in the first trimester to about 18 hours by the 38th week. By that point, a morning coffee is still partly there the next morning.
Some medications also interact with caffeine. If you take any regular prescription, ask your pharmacist whether it affects how you process caffeine.
How much caffeine is in common drinks
Caffeine content varies a lot by brand, brew strength and serving size. The FDA’s ranges for a 12-ounce serving:
| Drink (12 fl oz) | Approximate caffeine |
|---|---|
| Brewed coffee | 113 to 247 mg |
| Black tea | About 71 mg |
| Green tea | About 37 mg |
| Caffeinated soft drink | 23 to 83 mg |
| Energy drink | 41 to 246 mg |
For a sense of scale, the FDA says 400 mg a day is an amount not generally associated with negative effects for most adults. That’s a daily safety figure, not a sleep figure. You can stay well under 400 mg and still lose sleep if the timing is wrong.
Pure and highly concentrated caffeine powders and liquids are dangerous. The FDA warns that around 1,200 mg consumed quickly, less than half a teaspoon of pure powder, can cause toxic effects like seizures.
Can you flush caffeine out faster?
No. Water, exercise and more food don’t meaningfully speed up how your liver clears caffeine. Once it’s in, you wait. What you can do is stop adding more and plan tomorrow’s cutoff earlier.
If you’ve overdone it and feel jittery, the FDA lists the signs of too much caffeine as including a fast heartbeat, anxiety, jitters, upset stomach, headache and trouble sleeping. Chest pain, fainting or a racing, irregular heartbeat need urgent medical care.
What about cutting back?
If you drink caffeine daily and stop suddenly, expect withdrawal. MedlinePlus lists headaches, drowsiness, irritability, nausea and trouble concentrating, and says these usually go away after a couple of days. Moving your last cup earlier by an hour every few days is gentler than quitting outright, and it’s the timing, not the total, that matters most for sleep.
Pregnant, trying to conceive or breastfeeding? The FDA recommends talking to your health care provider about how much caffeine is right for you.
If caffeine timing is fixed and you still lie awake, the next step is our ranked list of ways to fall asleep faster, or work through the sleep hygiene checklist. More habit guides live in Habits and Routines.
Common questions
How long does it take for caffeine to wear off?
You'll usually feel caffeine for 4 to 6 hours, but with a half-life of about 5 hours, a quarter of a dose is still in your system around 10 hours after it peaks. Its effect on sleep outlasts the buzz.
Can 2 pm coffee affect sleep?
It can. A 2023 meta-analysis suggested finishing a regular coffee at least 8.8 hours before bed, so a 2 pm cup is borderline for an 11 pm bedtime and too late for an earlier one.
Does drinking water flush out caffeine?
No. Your liver clears caffeine at its own pace, and water or exercise don't meaningfully speed it up. The fix is an earlier cutoff tomorrow.
Why does caffeine last longer during pregnancy?
Pregnancy slows caffeine clearance. One review reports the half-life rising from about 5 hours early in pregnancy to about 18 hours by the 38th week. Talk to your health care provider about how much is right for you.
Written and checked by the Sleep Brief editors. We base every article on published research and guidance from medical bodies, and link the sources inline. How we research.
This article is for general education and isn't medical advice. If poor sleep lasts more than a few weeks, or you snore loudly, stop breathing in your sleep or feel sleepy while driving, talk to a doctor.
