Vitalicore • Tools • UK
Caffeine half-life calculator: estimate the amount left at bedtime
See how the time and amount of caffeine affect a simple bedtime estimate. Compare different half-life assumptions; no result is a personalised safe-sleep limit.
Estimate caffeine at bedtime
Enter the caffeine you consumed in the 24 hours before your intended bedtime. Include coffee, tea, energy drinks, pre-workout and relevant supplements. Use the pack or café information where available; drink strength varies.
Estimated caffeine remaining
Compare three assumptions
These are model scenarios, not a confidence interval or a safe-sleep threshold. Your actual response may differ.
The entered amounts exceed 400 mg in this window or include an entry above 200 mg. EFSA’s general healthy-adult intake figures are not personal targets or sleep limits. Consider total intake and seek individual advice about medicines or health conditions.
Midnight rule: a drink time later on the clock than your bedtime is treated as the previous day. For example, 23:30 before a 00:30 bedtime is one hour earlier. Equal clock times mean zero hours earlier. Do not enter future drinks.
What this calculator means
It adds the estimated remaining caffeine from each entry using amount × 0.5^(hours elapsed ÷ half-life). With 100 mg taken ten hours before bedtime, a five-hour assumption gives 25 mg remaining. With a slower assumption, the estimate is higher.
This simple model ignores absorption time, drinks earlier than the 24-hour window and differences in metabolism. It cannot measure a blood level, predict when you will fall asleep, diagnose insomnia or find a universally safe time for your last coffee.
Why the half-life setting matters
EFSA describes wide variation in healthy adults, approximately two to eight hours, with an average around four hours. Medicines, pregnancy, liver health and other factors can alter processing. The tool allows two to ten hours to illustrate assumptions; the ends of that input range are not biological limits.
Changing the setting is a way to see sensitivity to the assumption. It does not identify which assumption is right for you. Avoid changing medicines or supplementing to “speed clearance”.
Turn the estimate into a useful observation
Use the estimate alongside a 14-day sleep diary. Record the amount and time of caffeine, the intended sleep time, night waking and next-day effects. Compare your own observations without treating a modelled number as proof that caffeine caused the problem.
NHS insomnia advice includes avoiding tea and coffee for at least six hours before bed. That is general sleep advice, not a guarantee that caffeine is gone after six hours. Persistent sleep difficulty or breathing symptoms need assessment.
Intake figures are different from sleep thresholds
EFSA’s caffeine assessment considers intake from all sources. General healthy-adult figures do not mean an amount is suitable for every person, or that consuming it near bedtime will not affect sleep. Read product warnings and ask a pharmacist about medicines or conditions.
Your entries and privacy
The calculator code processes entries in this page and does not save them or submit them to Vitalicore. Advertising and analytics on the website have their own behaviour, described in our privacy information. Reloading clears the calculator entries.
Related next steps
Sources and calculation basis
Frequently asked questions
Does the calculator show a safe caffeine level for sleep?
No. It models an approximate amount remaining, not a safe level or a prediction of whether you will sleep.
Can I enter several coffees or energy drinks?
Yes. Enter up to 12 caffeine entries from the 24 hours before bedtime, using their caffeine amount in mg.
How does it handle bedtime after midnight?
It calculates elapsed time within the previous 24 hours. For example, a 23:30 drink before a 00:30 bedtime is one hour earlier.