How long does caffeine stay in your system? Half-life, timeline and bedtime math

Caffeine stays in your system for many hours. Its half-life in healthy adults is about 5 hours, with a range of about 2 to 10 hours, so half of a dose is still in your blood 5 hours after you drink it and about a quarter remains after 10 hours. Most of a morning coffee is gone by bedtime, but an afternoon cup often is not.

This guide shows the timeline hour by hour, explains why the number differs so much between people, and does the bedtime math for a normal day of coffee. Every number below comes from the cited sources or from simple half-life arithmetic that you can check yourself.

How long does caffeine stay in your system?

Caffeine is eliminated by half roughly every 5 hours in a typical healthy adult. After five half-lives, about 25 hours at that pace, about 3% of the dose remains, which is close to fully cleared. In people with a slow half-life of 8 to 10 hours, meaningful amounts can still be present the next morning.

The half-life is the time it takes for the amount in your blood to fall by half. It does not mean the caffeine is gone after twice that time. Each half-life removes half of what is left, so the curve flattens out. The Institute of Medicine review of caffeine pharmacology reports a mean half-life of about 5 hours, with individual values from about 1.5 to 9.5 hours. StatPearls gives the same typical value of about 5 hours.

The table below applies the 5-hour half-life to one 100 mg dose, roughly one 8-ounce cup of brewed coffee. It treats the dose as fully absorbed at the start, so real values in the first hour are a little lower.

Hours after the dose	Caffeine left (5 h half-life)	Caffeine left (8 h half-life)
0	100 mg	100 mg
2	76 mg	84 mg
4	57 mg	71 mg
6	44 mg	59 mg
8	33 mg	50 mg
10	25 mg	42 mg
12	19 mg	35 mg
15	13 mg	27 mg
20	6 mg	18 mg
24	4 mg	13 mg

Calculated as dose x 0.5^(hours / half-life). Half-life values from the Institute of Medicine review and StatPearls.

Multiply by your real dose. A 200 mg energy drink leaves about 50 mg after 10 hours at a 5-hour half-life, and about 84 mg at an 8-hour half-life.

How fast does caffeine kick in?

Caffeine is absorbed quickly from the gut. Peak blood levels occur between 15 and 120 minutes after you drink it, according to the Institute of Medicine review. The review links the spread mainly to differences in how fast the stomach empties, which food in the stomach can change.

After the peak, the decline follows the half-life. That is why the timing of a drink matters more than its size for sleep: a moderate dose late in the day can leave more at bedtime than a large dose in the morning.

What is the half-life of caffeine?

The half-life of caffeine is the time your body needs to clear half of the caffeine in your blood. For most healthy adults it is about 5 hours. Published individual values run from about 2 to 10 hours. A half-life is a property of your body on a given day, not of the drink, so the same coffee lasts longer in some people than in others.

Caffeine is cleared mainly by the liver. StatPearls describes the main pathway through the liver enzyme CYP1A2. How active that enzyme is in you sets most of your personal half-life. Genes, hormones, smoking, some medicines and liver health all change it.

Why does caffeine last longer for some people?

Your liver enzyme activity sets the pace. Smoking speeds caffeine clearance, so smokers often have a shorter half-life. Pregnancy and oral contraceptives slow it, so the half-life gets longer. Some medicines and liver disease also slow clearance. Genetic differences in CYP1A2 explain why two people who drink the same coffee can have very different nights.

Factor	Direction	What it means in practice
Smoking	Faster clearance	Shorter half-life; caffeine wears off sooner
Oral contraceptives	Slower clearance	Longer half-life; consider an earlier cutoff
Pregnancy	Slower clearance, most in late pregnancy	Longer half-life; follow the lower daily limit below
Liver disease	Slower clearance	Longer half-life; ask your doctor
Some medicines that block CYP1A2	Slower clearance	Ask your pharmacist about interactions
Genetic variation in CYP1A2	Either direction	Explains much of the person-to-person spread

Factors from StatPearls and the Institute of Medicine review. Direction only; individual effects vary.

You can not test your half-life at home, but you can observe it. If a 2 p.m. coffee makes it hard to fall asleep at 11 p.m., your half-life is probably at the slow end, or your sleep is sensitive to small amounts. Either way the practical answer is the same: move the last cup earlier.

How much caffeine is still in your body at bedtime?

Add up what each drink leaves at your bedtime. With a 5-hour half-life, a typical three-drink day (coffee at 8 a.m., coffee at 1 p.m., espresso at 4 p.m.) leaves about 60 mg at 11 p.m. With an 8-hour half-life, the same day leaves about 100 mg. That is the amount EFSA says can affect sleep in some people when taken close to bedtime.

Here is the math for that day. Caffeine amounts use USDA values: about 95 mg in an 8-ounce brewed coffee and about 63 mg in a 1-ounce espresso. See the full list in our caffeine in coffee and tea chart.

Drink	Time	Dose	Left at 11 p.m. (5 h half-life)	Left at 11 p.m. (8 h half-life)
Brewed coffee, 8 oz	8:00 a.m.	95 mg	12 mg	26 mg
Brewed coffee, 8 oz	1:00 p.m.	95 mg	24 mg	40 mg
Espresso, 1 oz	4:00 p.m.	63 mg	24 mg	34 mg
Total		253 mg	about 60 mg	about 100 mg

Calculated with the half-life formula above. Doses from USDA FoodData Central values for brewed coffee and espresso.

Two lessons come out of this table. First, the late drink matters most even when it is the smallest. The 4 p.m. espresso leaves as much at bedtime as the 1 p.m. coffee. Second, the morning coffee barely matters. If you want to cut caffeine at night, move or drop the last drink, not the first.

How long does each drink take to wear off?

The bigger the dose, the longer it takes to clear. With a 5-hour half-life, a single espresso (about 63 mg) falls below 25 mg in under 7 hours, a regular 8-ounce coffee (about 95 mg) in under 10 hours, and a large energy drink at the top of the FDA range (328 mg) only after about 18.5 hours.

The 25 mg line in the table is an illustration, not a safety threshold. It is a quarter of the roughly 100 mg that EFSA says can affect sleep in some people close to bedtime. The point is the comparison between drinks and between fast and slow half-lives.

Drink (typical dose)	Hours until below 25 mg (5 h half-life)	Hours until below 25 mg (8 h half-life)
Green tea, 8 oz (28 mg)	About 1	About 1.5
Black tea, 8 oz (47 mg)	About 4.5	About 7.5
Espresso, single (63 mg)	About 6.5	About 10.5
Brewed coffee, 8 oz (95 mg)	About 9.5	About 15.5
Espresso, double (126 mg)	About 11.5	About 18.5
Brewed coffee, 12 oz, high end (247 mg)	About 16.5	About 26.5
Energy drink, 16 oz, high end (328 mg)	About 18.5	About 29.5

Calculated as half-life x log2(dose / 25 mg). Doses from USDA FoodData Central and FDA ranges.

Two patterns stand out. Tea clears quickly because the dose is small. Large café coffees and energy drinks can still be above that line the next morning for slow metabolizers, which means caffeine from one day can carry into the next night. If you drink large sizes, the cutoff time matters more than for a single espresso.

How long does caffeine last during pregnancy or on the pill?

Longer than average. Pregnancy and oral contraceptives slow the liver enzyme that clears caffeine, so the half-life gets longer and the same coffee stays in the body for more hours. EFSA sets a lower daily limit of 200 mg during pregnancy and breastfeeding. The FDA recommends asking your health care provider whether you need to limit caffeine.

In practice, use the slower column of the tables above as your planning case, and move your last drink of the day earlier. If you are pregnant, discuss your total daily intake with your doctor or midwife, including tea, soft drinks and energy drinks, not only coffee.

How does caffeine affect sleep?

Caffeine taken later in the day is associated with shorter and lighter sleep. A 2023 meta-analysis of 24 studies found that caffeine reduced total sleep time by about 45 minutes and sleep efficiency by 7%, increased the time to fall asleep by about 9 minutes and reduced deep sleep by about 11 minutes. The effect depends on the dose and the time.

The two key studies give different but compatible answers:

• Drake et al., 2013: 400 mg of caffeine taken 6 hours before bed still reduced total sleep by about 1 hour compared with placebo. Doses at 3 hours and at bedtime also disturbed sleep.
• Gardiner et al., 2023: to avoid a loss of total sleep time, a 107 mg coffee should be had at least 8.8 hours before bed, and a 217.5 mg pre-workout serving at least 13.2 hours before bed.

Some people say they sleep fine after an evening espresso. They may fall asleep, but the meta-analysis found more time awake after sleep onset (about 12 minutes) and less deep sleep. Those changes are hard to notice from the inside. A sleep tracker can show a pattern over several weeks that one night can not. For the details of cutoff times, read when to stop caffeine before bed. For how sleep quality is scored, see what a sleep score measures.

How much caffeine is safe per day?

For most healthy adults, up to 400 mg of caffeine a day is not generally associated with negative effects, according to the FDA. EFSA reached the same daily figure and added that single doses up to 200 mg raise no safety concerns for healthy adults. During pregnancy and breastfeeding, EFSA sets the limit at 200 mg a day. Sensitivity varies, so lower can be better for you.

Group	Daily amount	Source
Most healthy adults	Up to 400 mg	FDA; EFSA
Single dose, healthy adults	Up to 200 mg	EFSA
Pregnant or breastfeeding	Up to 200 mg	EFSA; FDA advises asking your health care provider
Close to bedtime	Around 100 mg can affect sleep in some people	EFSA
Rapid intake linked to toxic effects such as seizures	Around 1,200 mg	FDA

Limits from the FDA consumer update and the EUFIC summary of the EFSA opinion.

400 mg is about four 8-ounce cups of brewed coffee at 95 mg each. Energy drinks and pre-workout products can reach a large share of that in one serving. The FDA lists energy drinks at 54 to 328 mg per 16 ounces. Pure powdered caffeine is the main risk: the FDA warns that toxic effects can appear around 1,200 mg taken quickly, which is less than half a teaspoon of pure powder.

How long do caffeine withdrawal symptoms last?

Withdrawal symptoms usually start 12 to 24 hours after your last dose, peak at 20 to 51 hours and last 2 to 9 days, according to a review of 66 studies. Headache is the most common symptom, followed by fatigue, low energy, drowsiness, low mood, poor focus and irritability. Stopping doses as low as 100 mg a day can cause symptoms.

The same review found that the incidence and severity of withdrawal tend to rise with the daily dose. Because symptoms scale with dose, a gradual reduction is a reasonable way to cut down; ask your doctor if you have a health condition. Moving the last cup of the day earlier is an easier first step than quitting, and it targets the drink that matters most for sleep.

When should you see a doctor about caffeine?

See a doctor if you have chest pain, a racing or irregular heartbeat, fainting, or severe anxiety after caffeine, or if you take medicines or have a heart, liver or anxiety condition. The FDA lists fast heart rate, palpitations, high blood pressure, insomnia, anxiety, jitters, upset stomach, nausea and headache as signs of too much caffeine.

Call emergency services for seizures, confusion or chest pain after a large dose, especially from powders or concentrated products. If you are pregnant, trying to become pregnant or breastfeeding, the FDA recommends talking with your health care provider about whether to limit caffeine.

How can you estimate your own caffeine at bedtime?

Log the time and size of each drink, apply a 5-hour half-life, and add the amounts left at your planned bedtime. If you know you are a slow metabolizer, run the math again with 8 hours. Then check your sleep data over two to four weeks to see whether late-caffeine days line up with worse nights.

A simple routine:

1. Write down each caffeinated drink and the time you finished it.
2. Use the table in the chart article for typical doses, or the label for packaged drinks.
3. Apply the half-life formula, or use an app that does it for you.
4. Compare days with more than about 50 to 100 mg left at bedtime against days with less.
5. Move your last drink earlier by an hour at a time until the difference in your sleep data disappears.

This is an observation, not a test. Stress, alcohol and late meals also affect sleep, so look for a consistent pattern rather than one bad night. Our sleep debt guide explains how a few short nights add up.

How Svanu estimates caffeine at bedtime

Svanu lets you log coffee and other drinks in one tap with a time. From those logs it estimates how much caffeine is still active at your bedtime. The logs also go to Apple Health. The sleep screen separately suggests tonight's bedtime, worked back from your own median wake time and sleep need.

After enough days, the correlations view checks whether caffeine is associated with your sleep and recovery. It uses 30-day Pearson correlations with at least 14 paired days and only shows a result when p is below 0.05. The sentence you see is a fixed template, not AI-generated text, and it describes an association in your data, not a cause. All scores are computed on your iPhone. You can read more about the app on the Svanu home page.

Key takeaways

• The half-life of caffeine is about 5 hours in healthy adults, with a range of about 2 to 10 hours.
• A quarter of a dose is still in your blood after about 10 hours at a typical half-life.
• The last drink of the day matters far more for sleep than the first.
• A meta-analysis suggests a regular coffee needs at least 8.8 hours before bed, and a large pre-workout dose at least 13.2 hours.
• Up to 400 mg a day is the FDA figure for most healthy adults. During pregnancy, EFSA uses 200 mg.