Estimated caffeine remaining
LIVE ESTIMATE0
mg · modeled, not measured
A fresh start.
Log your first drink to see how it may carry into your evening.
Your daily rhythm
Good energy.
Better nights.
Know your caffeine. Make room for rest.
↗ Consumed today
0 mg
400 mg reference ceiling · not a goal
☾ At your bedtime
0 mg
At 11:00 PM · estimated
Your next move
Start with your sleep.
Set your bedtime and sensitivity, then try a drink in the planner. There’s no required caffeine target.
Your caffeine, over time
Yesterday’s intake counts, too.
EstimateSensitivity range
Today’s ritual
Amounts in coffee and tea vary. Use the product’s label when available.
Small shifts, supported by science
Timing is part of the dose.
A large morning dose can still matter at night. Plan for your next sleep, including naps or daytime sleep.
Read the sleep research ↗An empty stomach changes the timing.
Food can delay absorption. It does not cancel caffeine or reliably make an extra dose safer.
See the food study ↗Pause before the pour
What if I have another?
Compare a dose before you commit to it.
Try a scenario
The planner never logs automatically. Compare future doses up to 48 hours ahead; logging is for drinks you have already consumed.
Your comparison
The same night. Two choices.
—mg at sleep · without this dose
—mg at sleep · with this dose
Choose a time and dose.
Your estimate will include your logged intake and your settings.
These comparisons use a simple decay model. A low estimate does not guarantee unaffected sleep. Food changes onset; we do not invent a meal-specific dose multiplier.
The everyday situations
Notice your patterns
Your daily journal.
A record of your intake and how you felt.
Your last seven days
Calendar-day totals in your device’s timezone. No intake goal.
A quick check-in
Observations can reveal patterns; they do not diagnose your metabolism or prove cause and effect.
All logged drinks
Sleep & your caffeine
WHOOP sleep, recovery, and cycle data beside your logged intake.
Connect WHOOP in Your settings to see recent sleep here.
Caffeine at sleep is modeled from your journal and selected half-life. WHOOP sleep estimates do not measure caffeine or prove why you slept a certain way. Times use this device’s timezone.
Check-ins
Evidence over hype
Show me the science.
Interval is a transparent, research-informed planning tool for adults. It uses a curated evidence library, not an AI doctor or a live search of every study. We distinguish findings, uncertainty, and app design choices. Evidence reviewed November 5, 2026; not automatically updated.
There is no universally optimal caffeine dose or proven “sleep-safe” amount remaining. Lower doses and earlier timing can reduce exposure; sensitivity and health context still matter. Reference ceilings are not recommended targets.
Under the hood
For each logged dose, remaining caffeine = dose × 0.5(hours since dose ÷ half-life). We add the doses, including previous days. The default half-life is 5 hours; the shaded band compares your estimate with 3 and 7 hours (expanded to include your selected setting). It is a sensitivity illustration, not a confidence interval, and some people fall outside it.
This model assumes immediate absorption and first-order elimination. Oral caffeine takes time to absorb, so it can overstate caffeine in the body just after a drink. We do not model active metabolites, blood concentration, receptor sensitivity, pregnancy, medication interactions, or individual genes. The graph’s gauge uses 400 mg only as a visual scale; it is not a “good zone.”
Planner rules are cautious product choices: flag intake within 8 hours of sleep, high single doses (over 200 mg), totals above the selected daily ceiling, and a dose of at least 400 mg within 12 hours of sleep. The 8-hour buffer and your adjustable 25 mg bedtime comparison threshold are planning settings, not validated biological cutoffs. “Rolling 24 hours” includes all logged intake in that window; calendar-day totals reset at midnight, but your body does not.
Use your actual next intended sleep time, especially for shift work. Do not use this tool to decide whether you can drive, stay awake safely, or treat a condition. Talk with a clinician for pregnancy, breastfeeding, heart rhythm problems, significant anxiety, liver disease, or medication interactions. Severe symptoms such as chest pain, fainting, seizures, or a racing/irregular heartbeat need urgent medical help.
Your rhythm, your settings
Make it yours.
Start with sleep. Adjust assumptions without mistaking them for measurements.
Private by design
Your journal and settings stay in this browser’s local storage. No tracker analytics, external fonts, AI requests, or subscription. The optional WHOOP connection sends WHOOP data requests through this site’s server; your caffeine journal is not sent. Clearing browser data clears your journal. Private browsing may erase it when you close the window. Other devices and browsers do not sync.
Backups include health settings and notes. Keep them somewhere private. Imports replace the current journal after confirmation.
WHOOP connection
Not connectedBring your last 14 days of sleep into your journal: duration, sleep stages, sleep performance, recovery score, HRV, resting heart rate, and cycle strain.
Optional, read-only access to sleep, recovery, and cycles. Sign in on WHOOP’s site. Synced WHOOP data stays on this page until you reload; it is not included in journal backups.
Open this section on the hosted site to check the connection.
Use on your phone
Open the hosted link in Safari or Chrome. You can bookmark it; no app install is needed. For this downloaded version, open index.html in a browser. Local-file opening and storage support vary by phone, so static HTTPS hosting is the recommended way to use it daily.
There is no background monitoring or notification service. Reopen the page to see current estimates. Drinks and settings are editable through the journal and settings screens.