About this tool
Caffeine follows first-order pharmacokinetics, which means a fixed fraction is cleared per unit of time. The standard adult half-life of about 5 hours means that 200 mg drops to 100 mg after 5 hours, 50 mg after 10 hours, and 25 mg after 15 hours.
How it works
Time to threshold = half_life × log2(Dose / Threshold)
Sleep researchers consider 25 mg the rough threshold below which caffeine no longer measurably degrades sleep. Plan your last cup so you are below 25 mg by your target bedtime.
How to use the Caffeine Half-Life Calculator
The Caffeine Half-Life Calculator is a browser-based tool that runs entirely on your device. Inputs you enter never reach a server - all calculations happen client-side in JavaScript. This means:
- Privacy: nothing is logged, sent, or stored by 3Tej. Inputs disappear when you close the tab.
- Speed: results update as you type. No network round trip.
- Offline use: once the page is cached, it works without internet.
- No signup: no account, no email, no rate limits.
Step by step
- Enter your inputs in the form above. Each field is labeled with its unit (currency, percent, kg, etc.) and the expected range.
- Read the result as it updates. The number reflects the formula commonly accepted in Caffeine Half-Life-related calculations.
- Adjust to see sensitivity: change one input at a time and watch how the output moves. This is the fastest way to understand which variable matters most.
- Copy or screenshot the result for later reference. The page state persists for the session if your browser allows it.
When you would use this
- Quick estimates: when you need a number now and don't want to open a spreadsheet.
- Sensitivity analysis: testing how a result changes as inputs vary, before committing to a real-world decision.
- Comparison: running the same calculation with different inputs to compare options side by side.
- Learning: building intuition for how the underlying math behaves.
- Documentation: capturing a snapshot of inputs and outputs at a point in time.
Frequently asked questions
What is the half-life of caffeine?
In healthy adults the average plasma half-life of caffeine is about 5 hours. It can be as short as 2 hours in fast metabolizers or as long as 9 to 10 hours in slow metabolizers, pregnant women, or smokers (after smoking stops).
How much caffeine affects sleep?
Doses above roughly 25 mg of caffeine in your system at bedtime measurably degrade slow-wave sleep and total sleep time. Caffeine consumed up to 6 hours before bed has been shown to disrupt sleep architecture even when subjects do not feel wired.
Why does caffeine affect me longer than friends?
The CYP1A2 liver enzyme metabolizes caffeine, and genetic variants make some people clear it 2 to 3 times slower. Pregnancy, oral contraceptives, and certain medications can also extend half-life dramatically.
What is a typical caffeine dose?
A standard 240 mL cup of brewed coffee has 95 mg, an espresso shot 65 mg, a 355 mL energy drink 80 to 200 mg, and an 8 oz black tea 47 mg. Pre-workout supplements often contain 150 to 300 mg per serving.
Is the Caffeine Half-Life Calculator accurate?
The Caffeine Half-Life Calculator applies the standard formula for caffeine half-life. Accuracy is limited only by your input precision. For decisions with material consequences, use the result as a starting point and verify with a qualified professional or the relevant official source.
Is the Caffeine Half-Life Calculator free?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads that appear around the tool but not inside the calculation flow.
Are my inputs saved?
No. Inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but does not see what you type into the form.
Can I use the Caffeine Half-Life Calculator on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum guidance.
How do I report a bug or suggest improvement to the Caffeine Half-Life Calculator?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours and update calculators when rules or formulas change.
How accurate is the Caffeine Half-Life Calculator?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Caffeine Half-Life Calculator free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Does the Caffeine Half-Life Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
Can I share results from the Caffeine Half-Life Calculator?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another caffeine half-life tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.