Estimated remaining
Estimate0
mg
No caffeine logged
Log your first drink to see how it may carry into your evening.
Your daily rhythm
Today
Caffeine intake and sleep, in one place.
Bedtime estimate · syncing sleep schedule
Today’s intake
0 mg
400 mg reference ceiling · not a goal
Estimated at bedtime
0 mg
At 11:00 PM · estimated
Before your next dose
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 intake
Amounts in coffee and tea vary. Use the product’s label when available.
Keep it simple
Log it. Check bedtime. Carry on.
Log all caffeine sources, including pre-workout. Your bedtime estimate includes previous days.
Plan another drink Compare caffeine at bedtime ↗
Try your next drink
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
Sleep comparison
—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
Your WHOOP snapshot
Waiting for first sync
More WHOOP details
Your records
History
A record of your intake and how you felt.
Your last seven days
Calendar-day totals in your device’s timezone. No intake goal.
Daily 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
Reference library
Research & sources
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. Half-life evidence reviewed November 6, 2026; other 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.
Caffeine clearance
Half-life is not a countdown to zero
Half-life is the time it takes to eliminate half a dose. EFSA describes an average of about 4 hours and a 2–8 hour range in healthy adults. NIH describes about 4–5 hours. We use 5 hours as a general adult starting assumption, not your measured clearance.
With the 5-hour assumption, a 200 mg drink leaves about 100 mg after 5 hours, 50 mg after 10 hours, and 38 mg after 12 hours. Twelve hours is not a universal clearance time. Feeling less stimulated does not mean all caffeine is gone or sleep will be unaffected.
Genetics, smoking, pregnancy, some medicines, oral contraceptives, and liver health can change clearance. WHOOP sleep and recovery data do not measure caffeine or determine your half-life.
Sources: EFSA adult half-life overview · NIH caffeine overview · 2022 pharmacokinetics analysis
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 2-hour and 8-hour scenarios, reflecting the healthy-adult range described by EFSA (expanded to include your selected setting). It is a sensitivity illustration, not a confidence interval or a complete biological range. 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.
With WHOOP linked, automatic mode estimates your next bedtime from up to 7 recent main sleep start times using a median that handles midnight. This is an app prediction, not a WHOOP forecast. Naps are excluded. Without recent WHOOP sleep, we use your saved/default schedule and label it. Manual overrides are available in Settings, especially for shifts or naps. 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.
Preferences
Settings
Set your bedtime, manage WHOOP, and keep your data handy.
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 your journal, health settings, and notes. Favorites stay on this device and are not included. Keep backups 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. WHOOP updates automatically on opening and every 5 minutes while this page is visible. Synced data stays in page memory and is not included in 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.
WHOOP refreshes automatically while this page is open and visible. Sync pauses when the page is hidden or closed. There is no notification service. Drinks and settings are editable through the journal and settings screens.