How it works
Caffeine is metabolized exponentially. The most commonly cited average half-life in healthy adults is about 5.7 hours, though it ranges from roughly 3 to 8 hours depending on genetics, pregnancy, oral contraceptives, smoking status, liver function, and other factors.
The formula used is:
Remaining mg = Dose × 0.5^(hours since dose / 5.7)
At bedtime, the calculator shows the total caffeine still active in your bloodstream from the entered dose. If you had multiple doses, you would sum each one separately; this calculator models a single dose for clarity.
Limitations
Half-life varies widely between individuals. Some people metabolize caffeine slowly and feel effects for much longer; others clear it quickly. Tolerance, sleep debt, and other stimulants also change how caffeine affects you. Use this as a rough guide, not a precise prediction.