How this calculator works
This tool helps you plan when to consume caffeine based on when you need alertness and when you plan to sleep. Unlike simple half-life calculators, it uses two evidence-based advances:
- Dose-dependent cutoffs (Gardiner 2025): A 100mg coffee has no measurable sleep effect even 4h before bed, but a 400mg pre-workout disrupts sleep even 12h before bed. Most calculators ignore dose.
- Range-based output (IOM 2001): Caffeine half-life varies from 3–8+ hours across the population. We show a range (fast/average/slow metabolism) instead of a falsely precise single number.
Enter your bedtime, add alertness windows (e.g., "Morning focus 8–11am"), pick preferred drinks for each intensity, and get a timed schedule showing when to drink and how much caffeine remains at bedtime.
Key evidence
- Gardiner et al. 2025 (RCT, 7 conditions): 100mg caffeine — no measurable sleep effect at any timing (even 4h before bed). 400mg — sleep disruption at 12h, 8h, and 4h before bed.
- Drake et al. 2013 (J Clin Sleep Med): 400mg at 6h before bed reduced total sleep by ~1 hour, even when subjects felt unaffected (subjective–objective disconnect).
- Institute of Medicine 2001: Caffeine half-life in healthy adults averages ~5h, range 1.5–9.5h, driven largely by CYP1A2 genetics.
Important
- This tool provides educational estimates only — not medical advice.
- Caffeine metabolism varies widely (half-life 3–8+ hours). Your actual clearance may differ.
- If you have a health condition, take medication, are pregnant, or are unsure, consult a clinician.
- This tool does not diagnose sleep disorders or caffeine sensitivity.