Caffeine Half Life Calculator — evidence-based tool to check your caffeine half life. Includes formula, tips, and interpretation guide.
Caffeine remaining (mg) = Dose × 0.5^(hours elapsed ÷ 5)
This is a standard first-order pharmacokinetic decay model. The exponent (hours ÷ 5) represents elapsed time as a fraction of the half-life. Raising 0.5 to this power gives the proportion of the original dose remaining.
Worked example: 200mg at 08:00, half-life 5h → at 13:00 (5h later): 200 × 0.5^1 = 100mg. At 18:00 (10h): 200 × 0.5^2 = 50mg. At 21:00 (13h): 200 × 0.5^2.6 ≈ 33mg. Cut-off to sleep at 23:00: 200 × 0.5^3 = 25mg — below the 50mg threshold, so sleep should be minimally affected.