Updated
Caffeine declines gradually rather than disappearing at a fixed cutoff. With an assumed five-hour half-life, 100 mg becomes 50 mg after five hours and 25 mg after ten. This calculator adds the estimated remainder from every entry. It cannot tell you whether that amount will disturb your sleep or whether a dose is safe.
How to estimate caffeine left at bedtime
- 1Enter the caffeine amount in milligrams for each drink or product. Use its label or the supplier's information when available; cup sizes and recipes vary.
- 2Enter how many hours before bedtime you consumed each one, from 0 to 36 hours. For a 23:00 bedtime, a drink at 15:00 was eight hours earlier.
- 3Keep the five-hour half-life assumption or change it. Compare the bedtime total and the following 24 hours with all drinks moved two hours earlier.
What the caffeine half-life formula means
For each entry, remaining caffeine = amount × 2^(−hours elapsed ÷ half-life). The tool adds these estimates. A half-life is the time for the modelled amount to fall by half, so each further half-life removes half of what remains.
The model assumes immediate absorption and one constant elimination rate. Five hours is an illustrative starting point. The adjustable two to twelve hours is a scenario range, not a measured personal range or a boundary covering everyone. The FDA notes wide variation in elimination and sensitivity.
Example: two drinks before bed
At a five-hour half-life, 100 mg taken ten hours before bed contributes 25 mg. Another 100 mg taken five hours before bed contributes 50 mg. The bedtime estimate is 75 mg. Moving both drinks two hours earlier gives about 57 mg, using the same assumptions.
What this estimate cannot tell you
- It estimates caffeine amount, not blood concentration, alertness or sleep quality. Absorption takes time, so very recent drinks are especially simplified.
- Medicines, health conditions and individual differences can change the result. Pregnancy and other circumstances can require separate advice about caffeine intake.
- Only logged entries count. A small estimated remainder does not establish a safe dose or a reliable coffee cutoff.
Common questions
Does a five-hour half-life mean caffeine is gone after five hours?
No. Half remains in this model. After two half-lives a quarter remains, and after three an eighth remains. The curve approaches zero gradually.
Can this tell me when to stop drinking coffee?
It can compare timing scenarios, but cannot identify a personal sleep threshold. Use the result to understand timing alongside your sleep observations, not as a guarantee.
Can I include tea, energy drinks or supplements?
Yes. Enter their caffeine amount in milligrams. The calculation uses the amount and timing, regardless of the product name.