Caff ConsciousCaffeine half-life calculator
How much of one drink’s caffeine could remain at bedtime? Change the amount, timing, and assumed half-life to explore an estimate.
The interactive calculator needs JavaScript to load. The worked example and formula below are available at any time.
Check your inputs. Bedtime must be at or after the drink time; choose “Next day” for a bedtime after midnight.
Estimated caffeine remaining at bedtime
Your inputs are calculated in this browser. They are not sent to a server or saved by this calculator.
A worked example
For an illustrative 100 mg drink at 2 PM and an 11 PM bedtime, nine hours pass. With a five-hour half-life, the model estimates 28.7 mg remaining. Changing the assumed half-life to six hours raises the estimate to 35.4 mg. Both answers depend on the assumption you choose.
How this calculator works
Remaining caffeine = starting caffeine × 0.5(hours elapsed ÷ half-life)
Half-life is the time for an amount to halve. This is the same first-order elimination equation used for an immediate drink in Caff Conscious. This web tool handles one drink with a fixed half-life; the app can account for your logged drinks, sipping windows, and selected metabolism settings.
CDC/NIOSH describes caffeine’s half-life as about five to six hours, while noting that it can remain in the body much longer. The FDA explains that sensitivity and elimination speed vary between people. Adjusting this input explores assumptions; it does not determine your personal half-life.
What the estimate leaves out
- Other drinks and caffeine remaining from earlier days.
- The time it takes to drink and absorb caffeine: this example assumes the whole amount enters at the selected time.
- Individual factors such as medications, health conditions, and pregnancy.
- Clock changes: these are wall-clock times on the same or next day, without daylight-saving adjustments.
The result is not a blood test, medical advice, a safe-caffeine threshold, or a prediction of sleep quality. For personal advice about caffeine and a medical condition, medication, or pregnancy, talk with a health professional.
Explore the timing
Read how long caffeine stays in your system for a half-life timeline, or caffeine before bed for a comparison of earlier and later drinks.