Caffeine Half Life Calculator
See how much caffeine is still in your body at any hour, when it will be low enough for sleep, and the latest time you can have your next cup. Add every coffee, tea or energy drink, and adjust for smoking, pregnancy, birth control, liver health and medicines that change how fast caffeine leaves your system.
Written and fact-checked by Manzoor Ahmad, Pharm-DLast reviewed October 2, 2026
Your caffeine today
What changes your half-life
These are the factors with the strongest evidence. Each one adjusts the average adult half-life of about 5 hours.
Add your drinks and bedtime to see how much caffeine is left when you go to sleep. Everything runs in your browser.
Caffeine left at bedtime
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Caffeine in your body over the day
Hour by hour
Each block is one hour. The outlined block is your bedtime.
Which drink is keeping you up?
How much of each drink is still in your body at bedtime.
Your half-life
Daily intake vs limit
How long one cup lasts for you
What is the half-life of caffeine?
The average half-life of caffeine in healthy adults is about 5 hours, meaning half of the caffeine you drink is still in your body 5 hours later. The normal range is wide, roughly 1.5 to 9.5 hours, and it can stretch well beyond that during pregnancy, with some medicines, or with liver disease.
So if you drink a 200 mg coffee at 3 pm, around 100 mg is still active at 8 pm and about 50 mg at 1 am. This caffeine half life calculator models every drink you have, adjusts for the factors that speed up or slow down caffeine clearance, and tells you how much is left at bedtime and the latest time you can have another cup.
How to use the caffeine half life calculator
- Add each drink with the time you had it. Choose from common coffees, teas, sodas, energy drinks and pills, or enter a custom amount in mg.
- Set your bedtime and your sleep-friendly level. Fifty milligrams, about half a cup of coffee, is a practical default; lower it if you are sensitive to caffeine.
- Answer the half-life questions. Smoking, the birth control pill, pregnancy, liver health and a few medicines have the biggest proven effects. If you know your own half-life from a test, enter it directly.
- Read the chart and results. You will see your peak caffeine level, the amount left at bedtime, the time it drops below your sleep-friendly level and your caffeine cutoff time.
How the calculation works
Caffeine is almost completely absorbed from the gut and broken down in the liver, mainly by the enzyme CYP1A2. Its level in the body follows a simple pharmacokinetic pattern: it rises as each drink is absorbed, peaks, then falls by half every half-life.
Caffeine remaining from one dose (after absorption)Remaining = dose × 0.5(hours ÷ half-life)
The calculator goes a step further than a basic half-life formula. It uses a one-compartment model with first-order absorption, the standard approach in pharmacology, so the curve includes the 30 to 90 minutes it takes caffeine to reach its peak. Absorption is faster on an empty stomach and slower with food or as a pill. Each drink is modeled separately and added together, so a morning coffee and an afternoon energy drink overlap the way they really do.
If you enter your weight, the calculator also estimates your peak blood level using a typical volume of distribution of about 0.7 liters per kilogram. That figure is a rough guide; individual values vary.
How long does caffeine stay in your system?
This chart shows how much of a 200 mg dose, about a large coffee, remains after absorption at different half-lives. A 5-hour half-life is typical; 3 hours is common in smokers; 8 hours fits many people on the birth control pill; 15 hours is typical late in pregnancy.
The half-life staircase
A 200 mg dose at an average 5-hour half-life
| Time after drinking | 3 h half-life | 5 h half-life | 8 h half-life | 15 h half-life |
|---|---|---|---|---|
| 2 hours | 126 mg | 152 mg | 168 mg | 182 mg |
| 4 hours | 79 mg | 115 mg | 141 mg | 166 mg |
| 6 hours | 50 mg | 87 mg | 119 mg | 152 mg |
| 8 hours | 31 mg | 66 mg | 100 mg | 138 mg |
| 10 hours | 20 mg | 50 mg | 84 mg | 126 mg |
| 12 hours | 12 mg | 38 mg | 71 mg | 115 mg |
| 16 hours | 5 mg | 22 mg | 50 mg | 95 mg |
| 24 hours | 1 mg | 7 mg | 25 mg | 66 mg |
Swipe sideways on a phone. It takes about five half-lives for roughly 97% of caffeine to be cleared: around 25 hours at an average half-life.
How long does it take for caffeine to kick in?
You may notice effects within 15 to 45 minutes, and levels typically peak 30 to 60 minutes after a drink on an empty stomach, or closer to 90 minutes or more with food or as a tablet.
How long does it take for caffeine to wear off?
The noticeable buzz usually fades in 3 to 6 hours, but caffeine is still present long after that. Even when you no longer feel it, the remaining amount can delay sleep and reduce deep sleep.
What affects caffeine half-life
Typical caffeine half-life by situation
Hours for half the caffeine to leave the body
| Factor | Effect on half-life | Typical half-life |
|---|---|---|
| Healthy adult, average | Reference | About 5 hours |
| Tobacco smoking | Speeds up CYP1A2, roughly 30 to 50% faster clearance | About 3 hours |
| Estrogen birth control pill | Slows clearance, close to doubling half-life | About 8 to 10 hours |
| Pregnancy | Rises through each trimester | Up to about 15 hours in the third trimester |
| Liver disease | Reduced breakdown | Can exceed 24 hours in cirrhosis |
| Fluvoxamine | Strongly blocks CYP1A2 | Increased about tenfold in clinical studies |
| Ciprofloxacin, cimetidine | Moderately slow clearance | Roughly 1.5 to 2 times longer |
| Genetics (CYP1A2 variants) | Fast or slow metabolizer | Varies person to person |
Effects combine. A pregnant smoker, for example, clears caffeine faster than a pregnant non-smoker.
Caffeine half-life during pregnancy
Pregnancy hormones slow caffeine breakdown, and the effect grows as pregnancy progresses, while the baby cannot clear caffeine efficiently. ACOG advises keeping intake below 200 mg a day during pregnancy. Choose the trimester in the calculator to see how long each drink lingers.
Caffeine and birth control
Estrogen-containing pills slow CYP1A2, so the same afternoon coffee can still be noticeable at bedtime. If you started the pill and suddenly sleep worse, moving caffeine earlier is a simple first step.
Caffeine content of common drinks
Caffeine by drink
Typical caffeine per serving
| Drink or product | Typical caffeine |
|---|---|
| Brewed coffee, 8 oz (240 mL) | About 95 mg (range roughly 80 to 100+) |
| Espresso, single 1 oz shot | About 63 mg |
| Cold brew, 16 oz | About 150 to 250 mg |
| Black tea, 8 oz | About 47 mg |
| Green tea, 8 oz | About 28 mg |
| Cola, 12 oz can | About 34 mg (diet versions about 46 mg) |
| Red Bull, 8.4 oz | 80 mg |
| Monster, 16 oz | About 160 mg |
| Caffeine tablet | Usually 100 or 200 mg |
| Decaf coffee, 8 oz | About 2 mg |
Amounts vary by brand, brew strength and serving size. Check labels for exact figures.
When should you stop drinking caffeine before bed?
A widely cited sleep study found that 400 mg of caffeine taken even 6 hours before bedtime reduced total sleep by more than an hour. For most people with an average half-life, stopping caffeine 8 to 10 hours before bed is a sensible rule, which means a cutoff in the early afternoon for a 10 pm bedtime. People with a longer half-life may need to stop earlier still.
The calculator’s “latest time for another cup” result does this math for you: it finds the last moment you could have a 95 mg coffee and still be under your sleep-friendly level at bedtime, taking everything you have already had into account.
How much caffeine is safe?
Healthy adultsUp to 400 mg a day is not associated with harmful effects for most people, according to the FDA and the European Food Safety Authority.
Single doseEFSA considers single doses up to 200 mg, about 3 mg per kg, safe for most adults.
Pregnancy and breastfeedingKeep below 200 mg a day during pregnancy. Caffeine also passes into breast milk, and young babies clear it very slowly.
Children and teensEFSA suggests up to about 3 mg per kg a day for children; many pediatric groups advise teens to avoid energy drinks.
Using caffeine to boost workouts? Sports nutrition research usually uses 3 to 6 mg per kg about an hour before exercise. Plan training sessions so that dose has time to clear before sleep, and explore more performance tools in the sport and fitness calculators collection.
A pharmacist’s notes on caffeine and medicines
Caffeine is the most widely used drug in the world, and like any drug it interacts with others. These are the situations I flag most often at the pharmacy counter.
Medicines that make caffeine last longer
Fluvoxamine is the big one: in clinical studies it increased caffeine’s half-life around tenfold, so a normal coffee habit can cause jitters, palpitations and insomnia. Ciprofloxacin and cimetidine have smaller but real effects. If you start one of these, consider cutting back on caffeine and see how you feel.
Medicines affected by caffeine
Caffeine and theophylline share the same breakdown pathway, so heavy caffeine use can raise theophylline levels. Caffeine can also worsen the jitteriness of decongestants and ADHD stimulants, and it is a hidden ingredient in some headache tablets. Check your medicine labels for caffeine when you add up your daily total.
Quitting smoking changes your caffeine
This surprises many people. Smoking speeds up caffeine breakdown, so when you quit, the same amount of coffee can roughly double in effect within days. Anxiety and poor sleep after quitting are sometimes partly a caffeine problem. Cutting coffee by about half when you stop smoking often helps.
Pre-workouts and caffeine pills
Concentrated caffeine products make it easy to overshoot. Pure powdered caffeine is especially risky because a tiny spoonful can contain a dangerous dose. Stick to measured products and count every source, including pre-workouts, energy drinks and caffeine gum. If you take regular medicines, the prescription refill calculator can help you keep track of them alongside your caffeine habits.
Signs you have had too much caffeine
- Jitters, shaky hands or restlessness
- Fast or irregular heartbeat
- Anxiety or irritability
- Upset stomach or nausea
- Trouble falling or staying asleep
Seek urgent care for chest pain, fainting, confusion, seizures or a very fast heartbeat, especially after caffeine pills or powders.
Body size also affects how caffeine feels: the same cup has a bigger effect on a smaller person. If you want to see where your weight sits for your height, try the BMI calculator.
Caffeine half life calculator FAQ
The average half-life of caffeine in healthy adults is about 5 hours, with a normal range of roughly 1.5 to 9.5 hours. It is shorter in smokers and longer during pregnancy, with the birth control pill, with liver disease and with certain medicines.
With an average 5-hour half-life, half of a dose remains after 5 hours, a quarter after 10 hours, and about 97 percent is cleared after roughly 25 hours. A 200 mg coffee at 3 pm still leaves about 50 mg at 1 am.
Caffeine remaining = dose × 0.5 raised to the power of (hours elapsed ÷ half-life). For example, 100 mg after 10 hours with a 5-hour half-life is 100 × 0.5² = 25 mg. This calculator also models absorption and adds up multiple drinks.
For most people, stopping caffeine 8 to 10 hours before bed is a good rule. A study found that 400 mg taken 6 hours before bedtime still cut sleep by more than an hour. The calculator works out your personal cutoff time from your drinks and bedtime.
Many people notice caffeine within 15 to 45 minutes. Levels usually peak 30 to 60 minutes after a drink on an empty stomach, and later when taken with food or as a tablet.
Pregnancy slows the liver enzyme that breaks down caffeine, and the effect grows through pregnancy, so half-life can reach about 15 hours in the third trimester. ACOG advises keeping caffeine below 200 mg a day during pregnancy.
Yes. Estrogen-containing birth control pills slow caffeine breakdown and can nearly double its half-life, so caffeine lasts longer and may disturb sleep more.
Yes. Tobacco smoke speeds up the CYP1A2 enzyme, making caffeine clear roughly 30 to 50 percent faster. After quitting smoking, the same coffee can feel much stronger within days.
Fluvoxamine can increase caffeine half-life about tenfold, and ciprofloxacin and cimetidine slow clearance moderately. Caffeine can raise theophylline levels and add to the effects of decongestants and stimulant medicines.
For healthy adults, up to 400 mg a day is generally considered safe, with single doses up to about 200 mg. During pregnancy the limit is 200 mg a day. Sensitive people may feel side effects at much lower amounts.
An 8-ounce cup of brewed coffee has about 95 mg of caffeine, though it ranges from roughly 80 to over 100 mg. A single espresso shot has about 63 mg, and a 16-ounce cold brew can contain 150 to 250 mg.
There is no reliable way to speed up caffeine clearance; time is what clears it. Light activity, water and food can ease jitters, but they do not meaningfully shorten caffeine's half-life.
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About the author
Manzoor Ahmad, Pharm-D
Pharmacist, health content writer and founder of DexoCalc
Manzoor is a Doctor of Pharmacy with more than nine years of experience writing about supplements, weight management and medication safety. He runs a community pharmacy where questions about caffeine, sleep and medicine interactions come up every week. He built this calculator from the original published equations and checks every formula against worked examples before release.
Sources and references
- Nehlig A. Interindividual differences in caffeine metabolism and factors driving caffeine consumption. Pharmacological Reviews. 2018;70(2):384-411.
- Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine. 2013;9(11):1195-1200.
- European Food Safety Authority. Scientific Opinion on the safety of caffeine. EFSA Journal. 2015;13(5):4102.
- U.S. Food and Drug Administration. Spilling the beans: how much caffeine is too much? Consumer update.
- American College of Obstetricians and Gynecologists. Committee Opinion No. 462: Moderate caffeine consumption during pregnancy.
- Abernethy DR, Todd EL. Impairment of caffeine clearance by chronic use of low-dose oestrogen-containing oral contraceptives. European Journal of Clinical Pharmacology. 1985;28(4):425-428.
- Jeppesen U, Loft S, Poulsen HE, Brøsen K. A fluvoxamine-caffeine interaction study. Pharmacogenetics. 1996;6(3):213-222.
- Guest NS, et al. International Society of Sports Nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition. 2021;18(1):1.
- Alcohol and caffeine: the perfect storm. PubMed Central.
This caffeine half life calculator gives estimates based on average pharmacokinetics. Your own response to caffeine depends on genetics, health and habits. It is not a diagnosis and not a substitute for advice from your doctor, pharmacist or dietitian. If you are pregnant, have a heart rhythm problem, anxiety disorder or liver disease, or take medicines, ask your doctor or pharmacist how much caffeine is right for you.