Caffeine calculator
When should you stop drinking coffee?
Caffeine has a half-life of roughly 5 hours in healthy adults. That 3 PM espresso is still ≈ 30 mg in your system at 11 PM — enough to push slow-wave sleep down measurably even when you fall asleep normally. Run your dose through the decay curve.
Caffeine decay curve
How the math works
Caffeine follows first-order elimination kinetics: a fixed fraction decays per unit time. The residual after t hours is dose × 0.5^(t / halfLife). The 50 mg threshold used as the "safe for sleep" line comes from controlled studies showing sleep architecture (slow-wave sleep, latency) is meaningfully affected above ≈ 100 mg residual at bedtime.
Half-life varies a lot between individuals: pregnancy nearly doubles it; oral contraceptives extend it 50%; smoking shortens it by ≈ 30%. CYP1A2 polymorphisms split the population into "fast" and "slow" metabolizers. Adjust the slider to match what you know about yourself, or default to 5h.
Sources: IOM, Caffeine for Mental Task Performance (2001)· Clark & Landolt, Sleep Med Rev 2017· Drake et al., J Clin Sleep Med 2013 (0/3/6h before bed RCT)
Related tools
- Sleep calculator — pair with cycle-based bedtimes
- Sleep latency tool
- Sleep debt tracker