Caffeine mg: Half-life Tracker

Log caffeine in one tap. Live Activity shows the time your body caffeine drops below the sleep-friendly threshold. No login. On-device only. No medical advice.

Caffeine mg is a one-tap caffeine tracker that visualises remaining body caffeine and the time it drops below a sleep-friendly threshold using a half-life decay model.

"Can I have one more coffee this afternoon and still sleep tonight?" — that's the question this app answers.

■ Who it's for

• Daily coffee or energy drink consumers
• People whose afternoon caffeine affects sleep
• Users who prefer no ads and one-time purchases
• Login-free, cloud-free, on-device-only data

■ Main features

• 50+ preset drinks (coffee, energy drinks, tea, etc.)
• Custom drinks with caffeine content and serving size
• Tap to log "now", long press to set the time
• Today's total intake and remaining allowance (400mg default)
• Half-life decay simulation
• Home screen widget for one-tap logging
• Siri / Shortcuts support
• Last 7 days of history

■ iOS 18 features (Pro)

• Live Activity + Dynamic Island for body caffeine + sleep-friendly time
• Lock Screen Control + Control Center for one-tap logging
• Action Button on iPhone 15 Pro and later
• Half-life simulation chart

■ Pro (one-time, JPY 370)

• Unlimited custom drinks
• Live Activity / Dynamic Island
• Lock Screen Control
• Action Button integration
• Full history + CSV export
• Medium / Large widgets

■ Why we made it

• Free to start (50+ presets + 3 custom drinks)
• No login, no account
• On-device only, never sent to cloud
• No subscription. Pro is one-time only.
• Zero ads.

■ Science

• Daily upper limit 400 mg (WHO / FDA / EFSA / Health Canada / Japan MHLW Sleep Guidelines 2023 consensus)
• 50 mg "sleep-friendly residual" threshold per Japan MHLW Sleep Guidelines 2023
• Default half-life is 5 hours (individual range 3-7 hours)
• All thresholds adjustable in Settings

■ Requirements

• iOS 18.0 or later (for Live Activity / Lock Screen Control / Action Button)

This app is intended as a caffeine intake tracker. It does not provide medical advice, diagnosis, drug-interaction checks, or individualised guidance for pregnant users, users with cardiac conditions, etc. Please consult a doctor or pharmacist for health decisions.