Caffeine Half-Life Sleep Calculator

Caffeine Half-Life Sleep Calculator

That afternoon coffee might still be affecting your sleep more than you'd think - this calculator estimates remaining active caffeine in your system.

Remaining Caffeine = Initial Dose x 0.5^(Hours Elapsed / Half-Life)

Example

100 mg consumed, 8 hours ago, 5-hour half-life:

Remaining = 100 x 0.5^(8/5) = ~33 mg still active

Why Half-Life Varies So Much Between People

Caffeine's average half-life in adults is commonly cited around 5 hours, but it varies significantly by individual metabolism, ranging roughly 3-7 hours - factors like liver enzyme activity, pregnancy, and certain medications can all shift this considerably in either direction.

Why the "6-8 Hour Rule" Exists

This calculation is exactly why the widely repeated advice to avoid caffeine within 6-8 hours of bedtime exists - even a full half-life or two after consumption, a meaningful amount of caffeine can still be biologically active and interfering with sleep onset.