Interactive tool · Caffeine & sleep
Caffeine Cutoff Calculator
Caffeine doesn't vanish when the cup is empty — it clears slowly, on a half-life of roughly five hours, so an afternoon coffee can still be circulating at bedtime. This tool estimates how much of a given serving is left in your system when you try to sleep, and the last safe time to have it so residual caffeine stays under a common sleep-disruption threshold. It is an estimate, not a personal readout.
Read before you use this
This is an educational estimate, not medical advice. It uses a simple textbook decay model with a half-life you choose, but individual caffeine metabolism varies widely — your genetics (the CYP1A2 liver enzyme especially), pregnancy, oral contraceptives and other medications, smoking, and liver function can roughly double or halve how long caffeine lingers. The ~50 mg “sleep-disruption” figure is a rule of thumb, not a validated personal limit; sensitivity differs from person to person. For general intake, the FDA notes that about 400 mg of caffeine a day is generally safe for most healthy adults, but that does not apply to everyone. Treat every number here as a starting point to experiment with, not a prescription, and talk to a clinician about caffeine if you are pregnant, take medication, or have a heart, anxiety, or sleep condition.
Last safe time to drink it (to be under ~50 mg at bedtime)
5:52 PM
That is about 4.6 hours before your 10:30 PM bedtime. Drink the same serving any later and more than ~50 mg is likely still circulating when you try to sleep.
Drinking it at 3:00 PM leaves about 33.6 mg (35.4% of the dose) in your system at bedtime, 7.5 hours later. That's under the ~50 mg sleep-disruption rule of thumb.
- Stricter cutoff (≤ 25% of the dose left)
- 12:30 PM
- 10 h before bed (= 2 half-lives)
- Left at bedtime from your intake time
- 33.6 mg
- 35.4% of 95 mg after 7.5 h
The decay curve, in numbers
Starting from 95 mg, each half-life (5 h) halves what is left:
| Hours after drinking | Caffeine remaining | % of dose |
|---|---|---|
| 0 h | 95 mg | 100% |
| 5 h | 47.5 mg | 50% |
| 10 h | 23.8 mg | 25% |
| 15 h | 11.9 mg | 12.5% |
| 20 h | 5.9 mg | 6.3% |
How it is calculated. Caffeine clears by first-order (exponential) decay: remaining = dose × 0.5(hours ÷ half-life). The “last safe time” inverts that for a target threshold T: you must drink it at least half-life × log₂(dose ÷ T) hours before bed. Worked example: a 95 mg coffee with a 5 h half-life leaves 47.5 mg after 5 h and 23.75 mg after 10 h; to stay under 50 mg at bedtime you would drink it about 4.6 h before bed.
Why the timing matters
A cutoff time is the easy part. The reason late caffeine backfires — and the calmer alternatives to chasing the afternoon slump with another cup — are in these:
- The afternoon caffeine crash, explainedWhy a second coffee is the wrong lever — and what adenosine rebound really is.
- L-theanine for focus (and the caffeine combo)The amino acid that smooths caffeine's edge, kept honest.
- Dehydration brain fogThe quiet third factor stacked under the afternoon dip.
- Best cognitive-energy picks (2026)Our evidence-graded hub for energy and focus.
This calculator is informational and not medical advice. It performs simple pharmacokinetic arithmetic on the values you enter and does not account for your individual metabolism, body size, tolerance, other caffeine through the day, or any health condition or medication. Caffeine clearance varies widely between people. Talk to a licensed clinician about your caffeine use if you are pregnant, take medication, or have a heart, anxiety, or sleep condition.
Beyond caffeine timing
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