Caffeine Calculator | Daily Intake & Half-Life
Estimate caffeine from coffee, tea, energy drinks, soda, pre-workout, chocolate, and custom items. Compare intake with guidance, model bedtime caffeine, find a cutoff time, and log days.
Total intake
237 mg
Moderate
Daily guideline
400 mg
general adult
At bedtime
39 mg
estimated
Sleep quality
Good
39mg remaining
Caffeine Level Through the Day
Daily Log
Important note
This is a general adult estimate based on typical caffeine content and a 5-hour half-life. Individual sensitivity, pregnancy, medications, anxiety, and heart conditions can significantly change safe intake limits. Consult a healthcare professional for personalised guidance.
What Is the Caffeine Calculator?
Add every drink you've had today and the calculator tracks how much caffeine is still active right now — and at your target bedtime. It uses the standard pharmacokinetic half-life model: caffeine decays exponentially, with roughly half eliminated every 5 hours. That 200mg coffee at 2pm leaves about 50mg circulating at midnight.
Each drink gets its own decay curve. The calculator sums them to show your current active load and projects your bedtime level. Smokers clear caffeine roughly twice as fast; pregnant women roughly half as fast. Adjusting the half-life slider makes the projection more accurate for you personally.
Caffeine Calculator Formula and Method
Remaining caffeine = dose_mg × 0.5^(hours_elapsed ÷ half_life).
Total caffeine at any moment = Σ of all drinks' remaining amounts.
Standard half-life: 5 hours for most healthy adults.
Example: 200mg at 8am → 100mg remaining at 1pm → 50mg at 6pm → 25mg at 11pm.
How to Use
- 1
Click "Add Drink" and select your beverage. Pre-filled amounts: brewed coffee 95mg per 8oz, espresso 63mg per shot, black tea 47mg, green tea 28mg, energy drink 160mg, pre-workout 200mg. Override the mg value if your brand differs.
- 2
Set the exact time you consumed each drink. The calculator uses that timestamp to determine how far each dose has decayed — a coffee at 7:30am contributes far less to your current load than one at 11am.
- 3
Add every caffeine source: coffee, tea, supplements, headache medication (Excedrin has 65mg per tablet), and dark chocolate if you ate a meaningful amount. Missing sources cause underestimates.
- 4
Adjust the half-life slider from the default 5 hours if your metabolism is faster or slower. Smokers: 3-4 hours. Pregnancy: 9-11 hours. Some medications slow metabolism by 30-50%.
- 5
Enter your target bedtime. The calculator projects your caffeine level at that time, colour-coded green (under 50mg), amber (50-100mg), or red (above 100mg).
- 6
Check the timeline chart, which plots total active caffeine from your first drink through midnight. Afternoon second peaks are often why bedtime caffeine is higher than expected.
- 7
Compare your daily intake against the 400mg guideline shown below the chart. The FDA and Mayo Clinic cite 400mg as the general safe limit for healthy adults; the pregnancy guideline is 200mg.
- 8
If your bedtime level is too high, shift an afternoon drink earlier in the calculator. Moving a 2pm coffee to noon can nearly halve what's left at midnight.
Caffeine Calculator Example
A typical weekday: 16oz coffee at 8am (190mg), 8oz coffee at 10:30am (95mg), black tea at 2:30pm (47mg). Total daily intake: 332mg — within the 400mg guideline.
At an 11pm bedtime with a 5-hour half-life: the 8am coffee (15 hours) leaves 23.75mg; the 10:30am coffee (12.5 hours) leaves 16.8mg; the 2:30pm tea (8.5 hours) leaves 14.5mg. Total at bedtime: roughly 55mg — amber zone. Moving the afternoon tea to before noon drops that to around 25mg, well into the green.
Understanding Caffeine
How Caffeine Actually Works
Caffeine blocks adenosine receptors in your brain. Adenosine accumulates throughout the day and creates progressive sleepiness. Caffeine doesn't eliminate that pressure — it just prevents the signal from registering. When caffeine clears, accumulated adenosine floods the receptors, which explains the hard afternoon crash.
What the 400mg Guideline Doesn't Tell You
The 400mg figure is a population-level average from large-scale studies. Below it, healthy adults generally show no measurable harm. But it's not a personal safety guarantee — some people feel anxious at 150mg, others drink 600mg comfortably. Your threshold depends on your genetics, body weight, medications, and any underlying conditions.
The Half-Life Maths Most People Haven't Seen
A 5-hour half-life means half of any dose remains after 5 hours, a quarter after 10, an eighth after 15. That's 200mg at 2pm → 100mg at 7pm → 50mg at midnight → 25mg at 5am. Research in the Journal of Clinical Sleep Medicine found caffeine taken 6 hours before bed reduced total sleep time by more than an hour.
Caffeine Content: What You Might Not Know
Dark roast has slightly less caffeine than light roast by weight — the longer roast breaks some down. Drip coffee: 70-140mg per 8oz. Espresso: 63mg per shot. Black tea: 40-70mg. Green tea: 28-35mg. Pre-workout supplements are consistently underestimated — popular brands range from 150-350mg per scoop.
Why Your Friend Can Drink Espresso at 9pm
The CYP1A2 gene encodes the liver enzyme that breaks down caffeine. Fast metabolisers clear caffeine roughly twice as quickly as slow ones. Pregnancy stretches the half-life to 9-11 hours by the third trimester — the main reason the pregnancy limit is 200mg. If you can't drink coffee after 2pm without lying awake, slow CYP1A2 metabolism is the most likely reason.
Frequently Asked Questions
How much caffeine is in a cup of coffee?
Brewed drip coffee averages 95mg per 8oz, but ranges from 70-140mg depending on brew strength. A double-shot 16oz latte is roughly 126mg. Black tea: 40-70mg. Green tea: 28-35mg. Energy drinks: 80-300mg. Pre-workout: 150-350mg — always check the label.
What time should I stop drinking coffee?
Stop 8-10 hours before you want to sleep. For an 11pm bedtime, that means cutting off around 1-2pm. A 200mg coffee at 2pm still leaves about 50mg active at midnight — enough to reduce deep sleep quality. Slow metabolisers should move the cutoff earlier.
Why does coffee stop affecting me?
Regular use causes your brain to grow more adenosine receptors, so the same dose blocks a smaller proportion. The alertness boost fades within days of consistent use. What doesn't fully adapt is caffeine's effect on sleep — even tolerant users show measurable reductions in deep sleep quality from residual caffeine.
Is 400mg of caffeine per day safe?
For healthy, non-pregnant adults, yes — 400mg is the threshold the FDA, EFSA, and Mayo Clinic cite as generally safe. But it's a population average. Some people feel anxious at 150mg. Pregnant women should stay under 200mg, as the fetus can't metabolise caffeine at all.
Does caffeine affect sleep even if I fall asleep fine?
Yes. Caffeine suppresses slow-wave (deep) sleep, the most physically restorative stage. You can fall asleep normally with 50mg still active and sleep through the night — but wake less rested because deep sleep was compressed. Falling asleep and getting restorative sleep are different things.
What's the half-life of caffeine?
About 5 hours for most healthy non-smoking adults. The real range is 2-9 hours depending on genetics, smoking, pregnancy, and medications. Smokers: 3-4 hours. Pregnancy (third trimester): 9-11 hours. Adjust the half-life slider in the calculator to match your situation.
Can I use this calculator if I'm pregnant?
Yes, but set the half-life slider to 9-10 hours — not the default 5. Caffeine metabolism slows significantly during pregnancy. The daily limit is 200mg (American College of Obstetricians and Gynecologists). Use this as a guide and consult your healthcare provider for personal advice.
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