Caffeine Half-Life Tracker

The Caffeine Half-Life Tracker shows how much caffeine is still in your body over the course of a day. Instead of treating a single cup of coffee in isolation, it lets you log every drink with its time, then sums the exponential decay of each one to plot a complete timeline. You can see your peak caffeine level, how much remains at bedtime, exactly when you are clear to sleep, and whether your day stays within the recommended limit.

What Is Caffeine's Half-Life?

The half-life of caffeine is the time your body needs to eliminate half of the amount present. For most healthy adults it averages about 5 hours, though it ranges roughly from 3 to 7 hours depending on the individual. After one half-life, half the caffeine remains; after two, a quarter; after three, an eighth, and so on. This is why caffeine fades gradually rather than disappearing all at once — and why a late-afternoon coffee can still be in your system at night.

The Caffeine Decay Formula

Caffeine clearance follows first-order exponential decay. The amount remaining after a time \(t\) is:

where \(C_0\) is the caffeine dose, \(t\) is the time elapsed, and \(t_{1/2}\) is the half-life. When you drink more than once, the total is simply the sum across every drink:

Each drink \(i\) only contributes once you have actually consumed it (when \(t \ge t_i\)). This superposition is exactly what the tracker does to build your curve.

Caffeine Content of Common Drinks

What Affects How Fast You Clear Caffeine?

Caffeine and Sleep

Caffeine keeps you alert by blocking adenosine, the brain chemical that builds up through the day and makes you feel sleepy. If a significant amount is still circulating at bedtime, it can delay how quickly you fall asleep and reduce the amount of deep, restorative sleep you get. Research suggests that consuming caffeine even 6 hours before bed can measurably disrupt sleep. This tracker uses your sensitivity setting to mark a sleep-safe threshold (25–100 mg) and tells you when your level drops below it.

How Much Caffeine Is Safe?

The US FDA considers up to 400 mg of caffeine per day safe for most healthy adults — about four 8 oz cups of brewed coffee. Pregnant people are generally advised to stay under about 200 mg per day. Individual tolerance varies widely, so treat these figures as general guidance rather than strict limits. The tracker shows your daily total against the 400 mg mark.

How to Use This Calculator

1. Log your drinks: For each drink, pick a common drink to auto-fill the caffeine amount (or type your own mg), then enter the time you drank it. Use "Add another drink" for as many as you need.
2. Set your half-life and bedtime: Choose a half-life preset that matches you (or enter a custom value) and set your target bedtime.
3. Choose your sensitivity: Low, normal, or high — this sets the sleep-safe caffeine threshold.
4. Track your caffeine: View your decay curve, peak level, the amount remaining at bedtime, your clear-to-sleep time, and a full hour-by-hour breakdown.

Frequently Asked Questions

What is the half-life of caffeine?

The half-life of caffeine is the time it takes your body to clear half of it. For most healthy adults it is about 5 hours, but it commonly ranges from 3 to 7 hours. Smoking shortens it to around 3 hours, while pregnancy, liver conditions, and oral contraceptives can lengthen it to 8 to 10 hours or more.

How long does caffeine stay in your system?

With a 5-hour half-life, half of a dose remains after 5 hours and about a quarter after 10 hours. It takes roughly five to six half-lives, or about 25 to 30 hours, to clear almost all of it. In practice a meaningful amount of caffeine can linger for 8 to 12 hours, which is why an afternoon coffee can still affect sleep.

How much caffeine is left in my body at bedtime?

It depends on how much you drank, when you drank it, and your personal half-life. This tracker adds up the remaining caffeine from every drink at your bedtime, so you can see whether the level is low enough for restful sleep.

Will caffeine affect my sleep?

Caffeine blocks adenosine, the chemical that makes you feel sleepy. Higher residual levels at bedtime can delay how quickly you fall asleep and reduce deep sleep. Sensitivity varies between people, so the same evening coffee may bother one person and not another.

How much caffeine is safe per day?

The US FDA considers up to 400 mg of caffeine per day safe for most healthy adults, which is roughly four cups of brewed coffee. Pregnant people are usually advised to stay under about 200 mg per day. Individual tolerance varies, so use these as general guidelines.

How can I get caffeine out of my system faster?

There is no reliable way to speed up caffeine metabolism. Drinking water, a short walk, and simply waiting help you feel better, but only time clears the caffeine. The most effective strategy is to avoid caffeine later in the day so less of it remains at bedtime.

Additional Resources

• Caffeine - Wikipedia
• Biological Half-Life - Wikipedia