How Long Does Caffeine Stay in Your System?

The average adult takes about five hours to break down half of the caffeine and it will take around 25 hours for all of it to be eliminated from the body. At this point, five half-lives have passed which is equivalent to 97 percent. Caffeine never reduces to zero as each half-life only breaks down half of what remains, not half of the original amount. Fast metabolizers take about 15 hours while slow metabolizers take 40 hours. For women in late stages of pregnancy this can take more than two days.

When should you stop drinking coffee before bed?

For the average person with normal caffeine metabolism it takes about 4.7 hours for a standard cup of coffee (96 mg) to fall below the 50mg threshold for good sleep. However, this is only true on days when nothing has been consumed. If you've already had two cups of coffee in the morning then most of your budget will be taken up by the remaining amounts throughout the day so you'll need to stop drinking at least 11 hours before bedtime. When entering the actual amount consumed, the tool calculates a result based on your individual half-life, bedtime and drink size.

How much caffeine can you have in a day before it becomes an overdose?

Health authorities have set a maximum daily intake for healthy adults at 400 mg, 200 mg during pregnancy and breastfeeding, and 3 mg per kilogram of body weight for children and adolescents. There is also an upper limit on the single dose of 200 mg. The latter is more important in terms of effects because symptoms are determined by the peak value rather than the daily total amount. A single energy drink can already reach this upper limit of the single dose.

Why am I more susceptible to caffeine than others?

This is usually due to the CYP1A2 enzyme, which metabolizes about 95% of caffeine. Due to genetic differences, people can be divided into fast metabolizers (about 40%), average metabolizers (45%) and slow metabolizers (15%). The half-life in slow metabolizers is 6–10 hours or longer. Smoking shortens the half-life by about half, while oral contraceptives lengthen it approximately twofold, and can extend it more than twice during late pregnancy. Sensitivity to the effects mediated through adenosine receptors also varies independently of clearance rate.

Does caffeine stay in your system for several days?

Yes. The cumulative amount can be fully calculated. If the same dose is repeated every 24 hours, all values are scaled by a factor of 1 divided by (1 minus 2 to the power of minus 24 divided by half-life). With an average half-life of five hours this factor is 1.037. So about four percent remains in the body until the next day but the cumulative amount is negligible. If the half-life is eight hours, then this factor is 1.14. In late pregnancy this rises to around 1.31 meaning that nearly a third of today's intake will be from yesterday.

How much caffeine can be dangerous?

It is usually stated that the amount which can be potentially lethal is between 150 and 200 milligrams per kilogram of body weight. For an adult person with a weight of 70 kg, this would mean 10.5 to 14 grams. This is where the known claim of 10 g comes from. That corresponds roughly to consuming 109 cups of extracted coffee at once. It is impossible to ingest that amount in one drink. Almost all documented cases relate to powder, tablets or concentrated drinks, as a few grams of substance fit into a tablespoon. Even a much lower single dose of about 6 mg per kilogram of body weight can cause unpleasant symptoms.

Does decaffeinated coffee really have no caffeine?

The "decaffeinated" label means that at least 97 percent of the caffeine has been removed. Therefore, a cup still contains about 2 to 15 mg. Although this is negligible for most people, drinking four cups of decaf coffee would be roughly equivalent to one cup of green tea. If you're on a limit of 200 mg during pregnancy or actually have slow metabolism, then you should consider that amount. Add this as another caffeine source and check the results yourself.

How much caffeine can I have during pregnancy?

ACOG, NHS and EFSA all recommend a daily maximum of 200mg. This is approximately two cups of instant coffee or one large cup of brewed coffee from a café. As CYP1A2 activity decreases during pregnancy and half-life may extend to between 11-18 hours later in the term, timing becomes more important than usual. At this rate caffeine from morning coffee can still be detectable when going to bed. So it is worth spreading your intake throughout the day. Consult a midwife or doctor rather than relying on a calculator tool.

Caffeine Calculator

What you drank

What do you want to work out?

All three run on the same decay curve. The difference is which question it answers and which fields it needs from you.

Today's caffeine, against a safe limit built for me

Sleep: what is left at bedtime, and when I should stop

One drink: how long it stays in my system

Caffeine source

Figures are USDA FoodData Central servings where one exists, otherwise the national food-agency value. Real drinks vary by a factor of two or more, so use the last row to type a number straight off a label.

Servings

Second source

Servings

Third source

Servings

Fourth source

Servings

Other source

mg each

Servings

Caffeine today

Room left before your limit

About you

Body weight

Whose limit should I use?

The adult figure is the FDA and EFSA number, the pregnancy figure is ACOG and NHS, and the per-kilogram figure for children is EFSA and Food Standards Australia New Zealand.

Healthy adult (400 mg a day)

Pregnant or breastfeeding (200 mg a day)

Teenager, 13 to 18 (100 mg a day)

Child under 13 (3 mg per kg of body weight)

I will set my own limit

How fast do you clear caffeine?

About 95 percent of caffeine is cleared by one liver enzyme, CYP1A2, and how much of it you make is largely genetic. If you are not sure, start on Average and move it if the answers do not match your experience.

I smoke tobacco

Tobacco smoke induces CYP1A2 and raises caffeine clearance by 50 to 70 percent, which roughly halves the half-life. Nicotine on its own does not do this, so patches and gum do not count.

Optional extras

What your numbers mean

96 mg is 24 percent of your 400 mg ceiling, leaving 304 mg spare.

That is roughly 3.17 more standard cups of brewed coffee before you reach it. Your day works out at 1.37 mg per kilogram of body weight.

Caffeine today (mg)

Your daily limit (mg)
Share of your limit (%)
Standard coffees still spare

Per kg of body weight (mg)
Biggest single serving (mg)
Safe single dose for you (mg)

Your half-life (h)

Charts and the hourly table

Show the caffeine level chart

Your estimated blood caffeine hour by hour, with the sleep threshold drawn across it.

Show me how my day compares with the published limits

Your total against your own limit and against the two figures every health agency publishes.

Show the hour-by-hour table

The same curve as numbers, which is easier to read off than a chart when you are picking a cut-off time.

Caffeine is the only psychoactive drug that most people consume daily, but often overlook its individual dose. It also has a slow elimination from the body which can lead to effects being misinterpreted easily. A cup of coffee is more than what you drink; it's a curve and the curve caused by a cup at 3pm continues until bedtime. This calculator answers three questions people often ask: How much have I consumed today? Is that a lot for my size? How much is still in me before bed? When should I stop drinking? And how long does an individual dose last?

The same formula supports all three modes.

In the normal range of dietary intake caffeine is eliminated from the body according to first-order kinetics. This means that a certain percentage rather than an absolute amount is eliminated per unit time. If t represents half-life then:

C(t) \;=\; D \times 2^{\,-t/T}

The amounts add up. The second cup of coffee has no knowledge of the first so at any given time in your body the amount is simply the sum of the individual caffeine amounts that have decayed according to how long they've been in your system.

C(t) \;=\; \sum_{i} D_i \times 2^{\,-(t - t_i)/T}

This accumulation is the core of this tool. A calculator that only simulates a single dose would not realize that the cup of coffee drunk at 7am could be responsible for pushing it over a limit before bedtime because it doesn't add up those curves. This makes the calculation very simple. Since every amount of caffeine is broken down at the same rate, the daily change after the last intake is an exponential function. So all questions about time can be answered with just one logarithm instead of simulating per hour.

Why it's 13 percent an hour.

With a typical half-life of five hours, after one hour of metabolism there will be 2 to the power negative one-fifth, or 0.8706, remaining in your system. So that's a per-hour decline of 12.9 percent, which is usually rounded up to 13. A dose of 200 milligrams of caffeine will remain at 87 milligrams after six hours and 50 milligrams after ten hours. It's the latter figure that matters, and it comes much later than most people think.

The half-life is a crucial factor.

About 95 percent of caffeine is broken down by the liver enzyme CYP1A2. The amount of this enzyme produced depends largely on genetics. People can be roughly divided into a few distinguishable groups.

Situation	Half-life	What changes
Fast metaboliser	about 3 hours	Wears off quickly, rarely wrecks sleep, you reach for the next one sooner
Average	about 5 hours	The figure nearly all published guidance assumes
Slow metaboliser	6 to 10 hours	One afternoon coffee is genuinely enough to cost you sleep
Late pregnancy	11 to 18 hours	CYP1A2 activity falls steeply; a morning coffee is still present at bedtime
Regular smoker	roughly halved	Smoke induces CYP1A2 and raises clearance by 50 to 70 percent
Oral contraceptives	roughly doubled	A well-documented interaction that almost no calculator offers

When you put those differences in numbers, it's no longer just an academic question. A person who takes 200 mg of caffeine at 2 p.m. and goes to bed at 10 p.m. will have 31 mg left if they're fast metabolizers, 66 mg if they're average, or 100 mg if they're slow. Even drinking the same cup of coffee at the same time can more than triple your exposure before bedtime. That's why calculators that assume a half-life of five hours are only accurate for about 45 percent of people.

How much caffeine is too much?

There are two boundaries that answer different questions, and confusing those two boundaries is the most common mistake on this topic.

Who	Per day	In one go	Source
Healthy adult	400 mg	200 mg	FDA, EFSA
Pregnant or breastfeeding	200 mg	200 mg	ACOG, NHS, EFSA
Teenager 13 to 18	about 100 mg	3 mg per kg	EFSA, paediatric guidance
Child under 13	3 mg per kg	3 mg per kg	EFSA, FSANZ

The daily intake refers to the long term exposure, while the single dose is the peak value and it's this peak that can cause heart palpitations and tremors in your hands. Even if you stay just under 400mg per day, a single energy drink could give you 200mg within ninety seconds leading to an unpleasant afternoon. This calculator shows both total intake as well as the maximum single dose value for this reason.

To adjust the calculation for changes in body weight, it is sensible to calculate per kilogram. At three milligrams per kilogram, the amount for children is 120 mg (at a weight of 40 kg) and for adults 240 mg (at a weight of 80 kg). This corresponds roughly to three cans of cola for a child or nearly four cups of instant coffee for an adult.

How much caffeine is actually contained in drinks?

The following values are based on the standard amounts from the USDA FoodData Central (for drinks where data is available). Consider these to be very rough averages. A single cup of brewed coffee can range in caffeine content between about 80 and 140 mg. Even for an identical 8 fluid ounce serving, actual amount will vary with type of coffee bean, grind size, and brew time.

Source	Serving	Caffeine	Notes
Brewed or drip coffee	8 fl oz / 240 ml	96 mg	Range 80 to 200 mg
Coffee-shop brewed coffee	16 fl oz / 470 ml	192 mg	Some chains reach 310 mg
Instant coffee	8 fl oz / 240 ml	62 mg	A large mug is nearer 100 mg
Espresso	one shot / 30 ml	64 mg	A double shot is 128 mg
Decaf coffee	8 fl oz / 240 ml	2.4 mg	Decaffeination removes 97 percent, not 100
Black tea	8 fl oz / 240 ml	48 mg	Rises with steep time
Green tea	8 fl oz / 240 ml	29 mg	Range 25 to 45 mg
Cola	12 fl oz / 355 ml	34 mg	Diet versions often higher, near 46 mg
Energy drink	8.4 fl oz / 250 ml	80 mg	Large cans reach 160 mg
Energy shot	2 fl oz / 60 ml	200 mg	A whole day's single-dose ceiling
Dark chocolate	50 g bar	25 mg	Milk chocolate about 10 mg

There are two other points worth revisiting: decaffeinated coffee does not necessarily contain no caffeine at all, and twelve cups of it contains about as much caffeine as a cup of green tea. Concentrates in energy drinks are the only everyday product that can achieve the maximum recommended single dose for adults with one sip.

Calculate the right time to stop drinking.

Many websites answer the question of when to stop drinking coffee with rules of thumb like six, eight or ten hours. The honest answer depends on three factors that those sites don't consider. And this calculator asks about those three factors.

First, set the value you want to hit before bed. Studies have shown that as little as 50 mg can cause measurable sleep disruption. However, some researchers argue that the goal should be zero because tolerance may mask but not prevent effects. Next, subtract out the caffeine already in your system. Any drinks you've had earlier in the day will gradually dissipate by bedtime. The remaining amount has already consumed part of your budget. Solving for when to drink a cup size C gives us this formula:

t_{\text{cut}} \;=\; t_{\text{bed}} \;-\; T \times \log_{2}\!\left(\frac{C}{\;\text{threshold} - R\;}\right)

Here R is the amount of caffeine left in your system from a drink you consumed earlier in the day by bedtime. If we consider a day with no caffeine consumption and set one cup of coffee at 96 mg, a threshold of 50 mg, and a half-life of 5 hours, then the result is 4.7 hours before bedtime. This is where the rule of thumb roughly hits it. So let's say you drink two cups of coffee at 7am and 10am and go to bed at 10pm. The two cups leave a total of 30.2 mg caffeine in your system, so there are only 19.8 mg left for the day, meaning that you need to stop consuming caffeine 11.4 hours before bedtime, or just after 10:30am.

Even for the same person, at the same threshold and with the same cup of coffee, the time to stop can vary by almost seven hours depending on what you've consumed before. A calculator that only considers the single dose won't pick this up.

Early drinking is cheaper

Whether you drink two cups of coffee at 7am or one cup at 7am and another at 2pm the total amount of caffeine is the same. What differs however is how much remains in your system by bedtime. If you go to bed at 10pm and have a half-life of 5 hours then from the two cups of coffee in the morning there will be 24.0mg remaining. With split intake there will be 43.7mg remaining, which is nearly double. This is because the afternoon cup does not take 15 hours to break down but only 8 hours. If you do not want to reduce your caffeine intake then it is most cost effective to consume the same amount earlier in the day if this is an option for you.

Does caffeine have a cumulative effect over several days?

Yes. The magnitude of this effect can be calculated and is not dependent on personal opinion. If you drink the same amount in a 24 hour period each day, then each day begins with the state at the end of the previous day. This sum is a geometric series which can be simplified as follows.

A \;=\; \frac{1}{1 - 2^{\,-24/T}}

Half-life	Build-up factor	What it means
3 hours (fast)	1.004	Nothing survives the night
5 hours (average)	1.037	About 4 percent carried over
8 hours (slow)	1.143	A seventh of your level is yesterday's
11.5 hours (late pregnancy)	1.308	Nearly a third is carried over

This is the basis for calculations that slow metabolizers complain about and fast metabolizers can never understand. At an average half-life of 24 hours, it's almost five half-lives so what you consumed yesterday has already been broken down. If the half-life is 11.5 hours, then it's only two half-lives which means that a third of what you feel this morning was consumed before the day started.

What this model doesn't take into account:

This model assumes that the intake is instantaneous. In reality it takes 30-60 minutes for caffeine to reach a maximum concentration in the blood and fatty meals can prolong this time. So the actual peak will be slightly later and lower than shown here. The value before bed is what most people want to calculate but this effect is small since the intake was already over hours ago.

This model also doesn't account for tolerance development and the effects of tolerance are in a negative direction. People who regularly consume caffeine will gradually feel less of an energizing effect from it, leading them to increase their intake but studies on brain activity still show reduced deep sleep phases. Just because you're feeling fine doesn't necessarily mean that the coffee you had late at night didn't have any effects.

This calculator is a population pharmacokinetic estimate and not medical advice. If you have caffeine sensitivity, anxiety or sleep disorders, are pregnant, taking medication, or have heart disease, please consult your doctor and do not rely on this website.

Frequently asked questions

How Long Does Caffeine Stay in Your System?: The average adult takes about five hours to break down half of the caffeine and it will take around 25 hours for all of it to be eliminated from the body. At this point, five half-lives have passed which is equivalent to 97 percent. Caffeine never reduces to zero as each half-life only breaks down half of what remains, not half of the original amount. Fast metabolizers take about 15 hours while slow metabolizers take 40 hours. For women in late stages of pregnancy this can take more than two days.
When should you stop drinking coffee before bed?: For the average person with normal caffeine metabolism it takes about 4.7 hours for a standard cup of coffee (96 mg) to fall below the 50mg threshold for good sleep. However, this is only true on days when nothing has been consumed. If you've already had two cups of coffee in the morning then most of your budget will be taken up by the remaining amounts throughout the day so you'll need to stop drinking at least 11 hours before bedtime. When entering the actual amount consumed, the tool calculates a result based on your individual half-life, bedtime and drink size.
How much caffeine can you have in a day before it becomes an overdose?: Health authorities have set a maximum daily intake for healthy adults at 400 mg, 200 mg during pregnancy and breastfeeding, and 3 mg per kilogram of body weight for children and adolescents. There is also an upper limit on the single dose of 200 mg. The latter is more important in terms of effects because symptoms are determined by the peak value rather than the daily total amount. A single energy drink can already reach this upper limit of the single dose.
Why am I more susceptible to caffeine than others?: This is usually due to the CYP1A2 enzyme, which metabolizes about 95% of caffeine. Due to genetic differences, people can be divided into fast metabolizers (about 40%), average metabolizers (45%) and slow metabolizers (15%). The half-life in slow metabolizers is 6–10 hours or longer. Smoking shortens the half-life by about half, while oral contraceptives lengthen it approximately twofold, and can extend it more than twice during late pregnancy. Sensitivity to the effects mediated through adenosine receptors also varies independently of clearance rate.
Does caffeine stay in your system for several days?: Yes. The cumulative amount can be fully calculated. If the same dose is repeated every 24 hours, all values are scaled by a factor of 1 divided by (1 minus 2 to the power of minus 24 divided by half-life). With an average half-life of five hours this factor is 1.037. So about four percent remains in the body until the next day but the cumulative amount is negligible. If the half-life is eight hours, then this factor is 1.14. In late pregnancy this rises to around 1.31 meaning that nearly a third of today's intake will be from yesterday.
How much caffeine can be dangerous?: It is usually stated that the amount which can be potentially lethal is between 150 and 200 milligrams per kilogram of body weight. For an adult person with a weight of 70 kg, this would mean 10.5 to 14 grams. This is where the known claim of 10 g comes from. That corresponds roughly to consuming 109 cups of extracted coffee at once. It is impossible to ingest that amount in one drink. Almost all documented cases relate to powder, tablets or concentrated drinks, as a few grams of substance fit into a tablespoon. Even a much lower single dose of about 6 mg per kilogram of body weight can cause unpleasant symptoms.
Does decaffeinated coffee really have no caffeine?: The "decaffeinated" label means that at least 97 percent of the caffeine has been removed. Therefore, a cup still contains about 2 to 15 mg. Although this is negligible for most people, drinking four cups of decaf coffee would be roughly equivalent to one cup of green tea. If you're on a limit of 200 mg during pregnancy or actually have slow metabolism, then you should consider that amount. Add this as another caffeine source and check the results yourself.
How much caffeine can I have during pregnancy?: ACOG, NHS and EFSA all recommend a daily maximum of 200mg. This is approximately two cups of instant coffee or one large cup of brewed coffee from a café. As CYP1A2 activity decreases during pregnancy and half-life may extend to between 11-18 hours later in the term, timing becomes more important than usual. At this rate caffeine from morning coffee can still be detectable when going to bed. So it is worth spreading your intake throughout the day. Consult a midwife or doctor rather than relying on a calculator tool.

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Disclaimer: This calculator is provided for general informational and educational purposes only. Our calculators are under active development, and results may be inaccurate, incomplete, or unsuitable for your situation. Always verify the figures independently and seek advice from a qualified professional before relying on them. We make no warranties and accept no liability for any loss or decision arising from use of this tool.

References

US Food and Drug Administration: Spilling the Beans, How Much Caffeine is Too Much?
The 400 mg a day figure for healthy adults, and the FDA's guidance on concentrated caffeine products.
EFSA Panel on Dietetic Products, Nutrition and Allergies: Scientific Opinion on the safety of caffeine (2015)
The European safety assessment: 400 mg a day and 200 mg in a single dose for adults, 3 mg per kilogram for children and adolescents, 200 mg a day in pregnancy.
American College of Obstetricians and Gynecologists: Moderate Caffeine Consumption During Pregnancy, Committee Opinion No. 462
The 200 mg a day pregnancy figure used by this calculator.
Nehlig A (2018): Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption
The Pharmacological Reviews survey of CYP1A2 variation, metaboliser phenotypes and the half-life ranges behind the metabolism selector.
Knutti R, Rothweiler H, Schlatter C (1981): Effect of pregnancy on the pharmacokinetics of caffeine
The measurements behind the extended half-life used for late pregnancy.
Parsons WD, Neims AH (1978): Effect of smoking on caffeine clearance
The 50 to 70 percent increase in clearance that the smoking switch applies as a halved half-life.
Drake C, Roehrs T, Shambroom J, Roth T (2013): Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed
The controlled trial showing measurable sleep disruption from caffeine taken six hours before bed, which is the basis of the sleep threshold.
Landolt HP (2012): No thanks, coffee keeps me awake, individual caffeine sensitivity depends on ADORA2A genotype
Why sensitivity to caffeine varies independently of how fast you clear it.
USDA FoodData Central
Source of the per-serving caffeine figures in the source list and the reference table.
NHS: Foods to avoid in pregnancy
The UK guidance limiting caffeine to 200 mg a day during pregnancy.
Food Standards Australia New Zealand: Caffeine
The expert working group finding of increased anxiety in children at about 3 mg per kilogram of body weight a day.