How long have you slept?
8 hours or more
Wake up time
Graph type
alertness (%)
Caffeine drink #1
Drink type
Filter coffee
Caffeine drink #2
Drink type
Filter coffee
Your alertness will be greatest at:
9:00am reaching 100.7%,
Alertness is a measure of your reflex and ability to stay focused. It equals 100% immediately after a full night of sleep. The higher it is, the better for you.

Thanks to the stimulating properties of caffeine, coffee is the number one drink when we're finishing a project or cramming before an exam. But how much and when exactly should you drink to make sure you'll remain focused until the end of the exam you've been studying for the entire night? Our calculator predicts the level of alertness and shows it as a cool visual graph, depending on the time you've slept and the dose of caffeine you've ingested. It uses a scientifically proven formula based on research on soldiers in the state of sleep deprivation. If you have a long night ahead of you, just choose one from the most popular caffeinated drinks and pick the time of each separate dose - your anticipated activeness level will be visualized below!

In the article you can find the formula used in the coffee kick calculator, how much caffeine a day you can have, and how much caffeine is in a cup of coffee. If you're interested, check out the caffeine intake calculator. And if you want to learn about different brewing methods to make a perfect coffee, try our coffee to water ratio calculator!

How to use the coffee kick calculator?

Every now and then we're forced to finish some work in a very limited time. Sometimes it's the nature of our job, sometimes a result of our procrastination - no matter the reason, it's a situation that requires extraordinary measures of action. Luckily, there's our coffee alertness calculator.

1. Enter how rested you are. Did you sleep well the whole night? Or maybe it was a very short night for you?

2. Decide what you want to see on the graph:

  • alertness - we assumed that your alertness is 100% immediately after a full night of sleep. Alertness is a measure of your reflex and ability to stay focused. The higher it is, the better for you;
  • response time - it's a negative measure of your reflex - the sleepier you are, the slower you react. It tells you how much time you need to respond to any stimulus. You surely want to keep it as low as possible;
  • reaction speed - it's a positive measure of your reflex - the more energetic you are, the higher your speed (mental and physical). As opposed to response time, you should keep it at a high level.

3. Input the time you've woken up.

4. Describe each consumed caffeine drink:

  • input the drinking time,
  • choose which drink you'll have,
  • enter the volume of your drink.

Or go to advanced mode and input the exact dose of caffeine in milligrams.

For a concentration of caffeine in certain drinks or their typical volumes, please check the table in the text below.

5. Every time you fill out one of the windows, another one will appear. You can plan your day with up to five different caffeine drinks.

6. The graph below the calculator shows your predicted alertness. Play with the number, time, and values of doses to see how the performance improves or drops!

The caffeine effect formula

The formula that we used in our calculator was developed by a team of scientists in the U.S. Army Medical Research and Materiel Command, Fort Detrick, Maryland. They described it in detail in the article titled A Unified Model of Performance for Predicting the Effects of Sleep and Caffeine. It turns out that about 40 percent of U.S. soldiers sleep only five hours a day (and even less in extreme situations such as combats) while the Centers of Disease Control and Prevention says that ordinary people need eight to nine hours of sleep. Scientists thus decided to conduct a research to keep the army in an excellent form throughout the day. Their studies lasted for over ten years, but they eventually found an applicable formula!

They assessed the soldiers' alertness using a unified performance test in 7 different sleep deprivation schedules: from 5 h of sleep per night to continuous sleep loss for 85 h. They tested 6 different caffeine doses: from placebo to repeated 200 mg doses to a single dose of 600 mg. They came up with a formula that accurately predicts group-average psychomotor vigilance task performance results! It works for a wide range of combinations of sleep schedules and caffeine dosage. In short, the formula helps find strategies to optimize neurobehavioral performance. Scientists claim that the algorithm they created (and which is used by our calculator) can improve performance and attention by 64%, while decreasing caffeine consumption by 65%. You can now predict how much caffeine you should drink, and when, to achieve peak alertness.

What is caffeine, actually?

Caffeine is the most popular psychoactive drug in the world, mostly recognized for its ability to alleviate fatigue. It's a chemical compound naturally found in coffee beans, tea leaves, and a few less known plants: kola nuts, guarana berries, and yerba mate leaves. According to the comprehensive review published in 2017 by an international team of scientists led by doctor Jennifer L. Temple,

Caffeine can influence objective and perceived cognitive performance by increasing alertness and wakefulness. (...) The impact of caffeine appears to be greater under conditions that would negatively impact performance, such as acute caffeine withdrawal or sleep deprivation.

Apart from mood elevation, energy boost, and arousal, caffeine has been proven to have a lot of positive influence on health! Its moderate consumption (up to 300-400 mg a day) is linked to lowered risk of:

  • stroke,
  • Congestive Heart Disease (CHD),
  • diabetes,
  • Parkinson's disease,
  • Alzheimer's disease,
  • and overall mortality!

How much caffeine is in a cup of coffee, tea, and energy drinks?

In coffee, the caffeine content depends on the kind of beans, roasting and brewing process. Similar principle accords to tea: different kinds of tea leaves, growing conditions, processing practices, and brewing techniques have an impact on the energizing properties of the drink. Energy drinks and shots, however, need to meet the standards, so you can count on them if you want a really accurate caffeine dosage. Check the value on the packaging. In the table below, you can find average caffeine contents of different kinds of caffeinated beverages. These are the numbers used in the calculator:

Drink type Caffeine content [g/L] Standard size Caffeine dose
in a portion [mg]
Espresso 1.5 1.7 fl oz (50 ml) 75
Filter coffee 0.6 8 fl oz (237 ml) 142.2
Instant coffee 0.4 8 fl oz (237 ml) 94.8
Latte / Mocha 0.34 8 fl oz (237 ml) 80.58
Decaf 0.04 8 fl oz (237 ml) 9.48
Covfefe 🤯 3 1 wall (2000 miles) powerful
Black tea 0.15 8 fl oz (237 ml) 35.55
Green tea 0.09 8 fl oz (237 ml) 21.33
Yerba mate 0.3 8 fl oz (237 ml) 71.1
Energy drink 0.33 8.6 fl oz (250 ml) 82.5
Yerba mate drink 0.2 17 fl oz (500 ml) 100
Energy shot 3.3 1.7 fl oz (50 ml) 165
Coke 0.1 12 fl oz (355 ml) 35.5
Diet Coke 0.13 12 fl oz (355 ml) 46.15

Of course "covfefe" isn't a real drink, it's just a joke 😂

How much caffeine a day can you have?

Scientists agree that 400 mg of caffeine is considered a maximum safe everyday dose. You'll find this much in three cups of strong filter coffee, five espressos, or ten small cans of Coke. The same review suggested that women of reproductive age shouldn't consume more than 300 mg caffeine per day and children should consume less than 2.5 mg per kilogram body weight (e.g., that makes 75 mg for a 30 kg child).

It's very hard to overdose on caffeine - death from its ingestion is very rare. Caffeine irritates the stomach, so ingesting it in really big doses would induce vomiting. Sure, overconsumption of products containing high levels of caffeine does bring patients to the emergency room. In most of these cases, the incident involves unusually high doses of caffeine (over 3 mg per kilogram body weight). Most deaths after caffeine intoxication are caused by overdoses of diet pills and stimulants, and most occur in young patients that don't know they have heart disease.

Signs that you're having too much

Some symptoms you may experience if you've drunk too much coffee can make you feel uneasy. Don't panic, they're going to pass, just don't drink another cup. You should watch for:

  • headaches - caffeine can trigger both light headaches and migraine attacks,
  • trouble falling asleep,
  • fast and strong heartbeat,
  • nervousness, irritability,
  • frequent urination and bowel movements,
  • stomach discomfort or heartburn (it's a sign of irritation of the stomach),
  • fluttering hands.

Remember that everyone metabolizes caffeine at a different speed - some people are more sensitive to it than others. If you don't drink caffeine regularly, you may be prone to experience more of its negative effects. The caffeine sensitivity can also depend on body weight, genetic inclinations, drug interactions, and health conditions.

What to do after sleep deprivation?

You probably feel exhausted, but if that's not the case, don't let yourself believe your organism took such effort lightly. Take a well-deserved rest! Plan it using sleep calculator. In your everyday routine, remember to get hydrated, exercise, and eat healthy. Make sure you don't strain yourself like this too often!

All GIFs used to illustrate this article come from the movie Coffee and Cigarettes by Jim Jarmusch. We don't approve of smoking cigarettes. Coffee is good on its own!

Małgorzata Koperska, MD and Dominik Czernia, PhD student

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Coffee Kick Calculator - How Much Caffeine to Drink to Stay Alert?