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Caffeine Half-Life Calculator

Caffeine has a half-life of roughly 6 hours. Calculate exactly when you need to stop drinking coffee today to protect your deep sleep tonight.

Your Biological Cutoff Time

11:00 AM

You must finish your drink by this time to ensure you have less than 25mg of active caffeine in your brain at bedtime.

Tired of doing the math?

The ARC app features a live, real-time SVG decay curve. Just tap what you drank, and watch the exact milligram count drop throughout the day.

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Are you a blogger or health coach? Copy the code below to add this tool to your website and help your readers protect their sleep.

<iframe src="https://arcapp.sbs/tools/caffeine-calculator" width="100%" height="600px" frameborder="0"></iframe>

The Science Behind the Calculator

Caffeine operates like a pharmaceutical with a specific half-life, typically around 5 to 7 hours for a healthy adult. This means 6 hours after you finish your coffee, exactly half of the caffeine is still active in your bloodstream, blocking adenosine receptors and preventing restorative deep sleep.

Why is my cutoff time so early?

To achieve high-quality sleep, your active caffeine levels should ideally be below 25mg at bedtime. If you consume a 200mg energy drink at 3:00 PM, you will still have over 80mg active in your system at 11:00 PM. Our calculator does the exponential decay math for you, ensuring you hit that zero-point exactly when you need to sleep.

How does this affect my Circadian Rhythm?

Caffeine doesn't give you energy; it borrows it from tomorrow. It binds to adenosine receptors (the chemical that makes you feel tired). When the caffeine finally wears off, all that built-up adenosine floods your receptors, causing a crash. Mismanaging this cycle disrupts your core temperature minimum and delays your natural melatonin release, throwing your entire circadian rhythm out of sync.

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