Tallywell.

Caffeine Cutoff Calculator

Enter your bedtime and today's drinks. You get the exact clock time for your last caffeine — computed from your own half-life, not a generic "stop by 2 PM".

Drinks already had today
Your metabolism

Finish your last drink by

—

At bedtime, you'll have left

DrinkTimeLeft at bedtime

How it's computed

One-compartment elimination: remaining = dose × 0.5(hours ÷ T½). Base half-life 5 h; smoking multiplies by 0.6, estrogen contraceptives by 1.8, self-reported slow metabolism by 1.3. Cutoff time solves dose × 0.5(Δ ÷ T½) = your bedtime limit. Individual half-lives in the literature run 1.5–9.5 h — which is exactly why generic advice can't give you a time.

  • Drake et al. 2013 — 400 mg taken 0, 3, and 6 h before bed each reduced objective sleep by about an hour.
  • FDA — 400 mg/day cited as safe ceiling for healthy adults.

See the curves: caffeine half-life, drawn · Log a full day: Caffeine Timeline