Black Tea (8 oz) Caffeine Half-Life & Bedtime Decay
Brewed black tea (English Breakfast, Earl Grey, Assam) contains 45–50mg of caffeine per 8oz cup, already sitting right at the sleep-safe threshold.
Interactive Stack Calculator for Black Tea (8 oz)
We've preloaded Black Tea (8 oz) (50mg) below. Adjust your planned bedtime or add other drinks to see your exact curve.
Caffeine Half-Life & Cutoff Calculator
Caffeine's half-life ranges from about 4 to 7 hours depending on how fast you metabolise it. Add what you've already drunk today to find the last time your next drink still leaves under 50 mg in your system at bedtime.
Caffeine Sensitivity
Not sure? If an afternoon coffee keeps you up at night, pick Slow.
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Last safe 50 mg drink
Calculated so that under 50 mg of caffeine is still circulating at bedtime, counting today's drinks.
Today's drinks alone leave about 8 mg at bedtime.
Solid: caffeine from today's drinks. Dashed: with one more drink at your cutoff, landing on the 50 mg line at bedtime.
Stop guessing your cutoff.
Here you type your drinks in. ARC does the same math from every drink you log in one tap, moves your last safe coffee the moment you log a cup, shows it as a live countdown, and tells you plainly when no cup fits any more.
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Black Tea (8 oz) Hour-by-Hour Caffeine Decay Table
Pharmacokinetic Decay (5.5h Half-Life)Exact milligrams of caffeine remaining in the bloodstream at 2-hour intervals if consumed at various times of day, based on an average human caffeine half-life of 5.5 hours. Target is less than 50mg active at 11:00 PM bedtime.
| Intake Time | +2 hrs | +4 hrs | +6 hrs | +8 hrs | +10 hrs | +12 hrs | At 11 PM Bed | Status |
|---|---|---|---|---|---|---|---|---|
| 08:00 AM | 39 mg | 30 mg | 23 mg | 18 mg | 14 mg | 11 mg | 8 mg | ✓ Sleep Safe |
| 12:00 PM (Noon) | 39 mg | 30 mg | 23 mg | 18 mg | 14 mg | 11 mg | 13 mg | ✓ Sleep Safe |
| 02:00 PM | 39 mg | 30 mg | 23 mg | 18 mg | 14 mg | 11 mg | 16 mg | ✓ Sleep Safe |
| 04:00 PM | 39 mg | 30 mg | 23 mg | 18 mg | 14 mg | 11 mg | 21 mg | ✓ Sleep Safe |
Cutoff Recommendation: Can safely be consumed until 5:30 PM without exceeding bedtime thresholds.
Values are calculated using the standard exponential decay model: mg_remaining = initial_mg * 0.5^(hours / half_life).
How Your Genetics (CYP1A2) Impact Black Tea (8 oz) Clearance
Over 95% of caffeine metabolism takes place in your liver via the cytochrome P450 enzyme CYP1A2. Depending on whether you carry the fast or slow metabolizing gene variant, clearance times for 50mg vary drastically:
Residual after 8 hours: 13 mg. You clear caffeine rapidly and rarely experience insomnia from lunch beverages.
Residual after 8 hours: 18 mg. Standard biological decay rate representing ~50% of the population.
Residual after 8 hours: 23 mg. CYP1A2*1F carriers. Any caffeine consumed past noon will disrupt sleep architecture.
Frequently asked questions
Will an afternoon cup of black tea affect sleep?
Because an entire cup is only 50mg, by bedtime (5 hours later) only about 26mg remains, which is well below the sleep-disruption threshold for most adults.