It's three in the afternoon. You had a cappuccino with breakfast and an espresso after lunch, and now your eyelids feel heavy and you're already eyeing the coffee machine. You start to wonder: is this one too many?
Here's the short answer. For most healthy adults, up to 400 mg of caffeine a day is considered safe by the European Food Safety Authority (EFSA), and the US Food and Drug Administration lands on the same 400 mg. Using EFSA's typical values, that's about five espressos. Whether you're close to that number is another story, and most of us have no idea.
So how do you know where you stand? You need three things: the limit, a rough idea of how much caffeine your drinks hold, and a sense of how long it hangs around in your body. That last part is the one people forget, and it's the one that ruins your sleep.
What's the daily caffeine limit?
The 400 mg figure comes from a big safety review that EFSA published in 2015. Its experts concluded that intakes of up to 400 mg a day, spread across the day, don't raise safety concerns for healthy adults. For an average adult, that works out to about 5.7 mg per kilogram of body weight.
The FDA uses the same number and translates it into American mugs. It says 400 mg is about two to three 12 fluid ounce cups of coffee. Wait, five espressos or three mugs? Both are right. A 12 ounce mug (about 355 ml) of brewed coffee holds anywhere from 113 to 247 mg, so a couple of big mugs can get you most of the way there before noon.
There are a few details that matter as much as the headline number.
How fast you drink it counts. EFSA says a single dose of up to 200 mg, about 3 mg per kilogram of body weight, doesn't raise safety concerns for healthy adults. So two strong coffees drunk one after the other land harder than the same two coffees spread over a morning. What matters here is how much you take in one sitting.
Pregnancy and breastfeeding lower the limit. If you're pregnant or breastfeeding, EFSA's limit is 200 mg a day from all sources. The FDA's advice for anyone pregnant, trying to get pregnant or breastfeeding is simple: talk to your health care provider about whether you should cut down.
Kids and teens have their own number. For children and adolescents, EFSA proposes 3 mg per kilogram of body weight per day. For a teenager who weighs 50 kg, that's 150 mg. One energy drink and a cola already get close. The FDA adds that too much caffeine in children and teens can cause a racing heart, anxiety and sleep problems.
Why these numbers and not others? They mark the level below which the experts found no reason for concern in healthy people. That's a ceiling for a typical body. Plenty of people feel jittery well before they get there, because how sensitive you are to caffeine and how fast you clear it vary a lot from person to person. If 200 mg already makes your hands shake, your personal limit is lower, and that's fine.
How much caffeine is in your drinks?
This is where most of us get it wrong. We count cups, and cups vary wildly.
EFSA publishes typical values for common drinks. Here they are:
| Drink | Serving | Caffeine |
|---|---|---|
| Espresso | 60 ml | about 80 mg |
| Filter coffee | 200 ml | about 90 mg |
| Black tea | 220 ml | about 50 mg |
| Cola | 355 ml | about 40 mg |
| Energy drink | 250 ml | about 80 mg |
Source: EFSA, caffeine topic page.
A few things jump out. The espresso tastes stronger, yet a regular cup of filter coffee has slightly more caffeine in it. A small energy drink carries about the same as an espresso. And a can of cola, which a lot of people never think of as a caffeinated drink, still adds around 40 mg. It brings sugar with it too, and we added up the sugar in everyday drinks in a separate guide.
Let's run a quick example. Two espressos and a can of cola over the day come to about 200 mg. Add a small energy drink before the gym and you're at 280. Nothing about that day feels excessive, and you're already at 70% of the adult limit.
Now the honest part: these are averages. Real drinks move around a lot. The FDA's figures for a 12 ounce serving show the spread clearly:
- Soft drinks: 23 to 83 mg
- Energy drinks: 41 to 246 mg
- Brewed coffee: 113 to 247 mg
Energy drinks vary the most from one brand to another, so the label is worth a look. Coffee changes with the beans and the way it's brewed, which is why two mugs from two different cafés can be far apart. Even decaf isn't zero: the FDA puts it at 2 to 15 mg in an 8 ounce cup. That won't matter to most people. It's good to know if you're very sensitive.
Caffeine and sleep: when should you stop?
Here's where timing comes in. Caffeine doesn't disappear when the buzz fades. Your liver breaks it down slowly, and the usual way to describe that speed is the half-life, meaning the time it takes for half of it to leave your blood.
In adults, caffeine's half-life is usually between 3 and 7 hours, according to a 2017 review in Frontiers in Psychiatry. Do the math with 5 hours, somewhere in the middle. An espresso at 4 pm puts about 80 mg in your system. By 9 pm, around 40 mg of it is still there. By 2 am, about 20 mg. You went to bed hours ago, and your body is still working through that afternoon coffee.
Your own half-life depends on a lot of things. During pregnancy it gets much longer, on average 8.3 hours longer. Smoking speeds up how fast you clear caffeine, and combined birth control pills slow it down. Genetics plays a big part too, which helps explain why some people can drink a double espresso after dinner and still sleep through the night.
How much caffeine does it take to affect sleep? Less than you'd think. EFSA notes that a single dose of 100 mg may affect how long and how well some adults sleep, particularly when it's consumed close to bedtime. That's about one cup of filter coffee.
The study most people cite on timing is Drake and colleagues, published in 2013 in the Journal of Clinical Sleep Medicine. They gave 12 healthy sleepers 400 mg of caffeine at bedtime, 3 hours before bed, or 6 hours before bed, and compared it with a placebo. All three timings disturbed sleep. Even when the caffeine was taken 6 hours before bed, total sleep dropped by more than an hour, as measured by a sleep monitor the participants wore at home.
The strangest finding? At 6 hours, the participants mostly didn't notice. Their sleep diaries showed no clear change. The sleep monitor recorded the lost sleep. So "coffee doesn't affect my sleep" may be true for you, or it may just mean you haven't seen the data.
A fair caveat: 12 people is a small study, and 400 mg in one go is a lot of caffeine. The lab measurement at 6 hours showed a smaller drop that only approached statistical significance. Still, the authors concluded that their results support avoiding substantial caffeine for at least 6 hours before bed.
What does that mean in practice? If you go to bed around 11 pm, try to have your last real coffee by 5 pm. If you're sensitive, or you've noticed you sleep lighter on busy coffee days, move it earlier, to lunchtime.
Signs you're having too much
Your body usually tells you when you've overdone it. According to the FDA, too much caffeine can cause:
- a faster heart rate or heart palpitations
- higher blood pressure
- trouble sleeping
- anxiety and jitters
- an upset stomach or nausea
- headaches
Most of the time these are mild and fade as the caffeine wears off. They're still worth paying attention to. If you get the jitters most afternoons, or you keep waking at 3 am, your intake is a good first place to look.
Serious problems tend to come from very large amounts taken quickly. The FDA estimates that toxic effects, such as seizures, can show up with rapid consumption of around 1,200 mg. With pure powdered caffeine, less than half a teaspoon can get you there. The FDA warns that these concentrated products can have serious health consequences, including death, so keep them out of your kitchen.
If your heart is pounding and won't settle, if you feel chest pain, or if you feel faint, stop drinking caffeine and get medical help. The same goes if you have a heart condition, take regular medication, or are pregnant: ask your doctor what amount makes sense for you.
How to keep count of your caffeine
Here's the problem with everything above. Keeping a running total of milligrams in your head, across a whole day of different drinks, is close to impossible. And the caffeine you had at 3 pm still matters at 10 pm, which a simple tally doesn't capture.
That's why we built Brimful. You log a drink, pick it from the database or create your own, and the app adds its caffeine to your day. You set a daily caffeine limit and see at a glance where you stand. Brimful also estimates how much caffeine is still in your system as the hours pass, using an average half-life of about 5 hours, so you can see whether that afternoon espresso will still be around at bedtime. The same log tracks calories, protein and sugar too.
Every figure in the app is an estimate, and your body won't follow the average exactly. Still, a week of honest logging tells you more than any guess. Often the surprise is a drink you never thought of counting.
So, how much is too much?
For a healthy adult, more than 400 mg a day, or more than 200 mg in one sitting, goes past the levels EFSA considers safe. If you're pregnant or breastfeeding, EFSA's level is 200 mg a day. For kids and teens it's 3 mg per kilogram of body weight. Below those numbers, pay attention to how you feel: if you're jittery, anxious or sleeping badly, you've found your limit, wherever it sits.
And watch the clock: caffeine from a late coffee can still be in your system at bedtime.
The takeaway: Keep your daily caffeine under 400 mg, have your last real coffee at least 6 hours before bed, and log what you drink for a week. You'll find out whether that third coffee of the afternoon is a habit worth keeping.
