Calculator

Caffeine Clearance Calculator

Model how caffeine moves through your system and find your personal cutoff time for sleep.

Coffee ~95mg, espresso ~63mg, energy drink ~80-200mg

Based on CYP1A2 genotype. If unsure, choose "Normal." Smoking and cruciferous vegetables increase clearance; oral contraceptives decrease it.

How this works

Caffeine is primarily metabolized by the CYP1A2 enzyme in the liver. Its elimination follows first-order kinetics with a half-life that varies significantly between individuals. The average half-life in healthy adults is roughly 5 hours, but CYP1A2 polymorphisms, smoking status, pregnancy, liver disease, and concurrent medications can shift this range from 2 to 12+ hours.

This calculator models caffeine plasma concentration over time using standard pharmacokinetic equations with absorption rate constant (ka) of 0.5/hr (Tmax ~45 min) and elimination half-lives calibrated to metabolizer status: fast (~3h), normal (~5h), slow (~8h).

Threshold for sleep disruption: Research suggests that plasma caffeine levels above approximately 1.0-1.5 mg/L (roughly 20-25% of peak from a standard dose) can measurably delay sleep onset and reduce sleep quality. This calculator flags when you drop below that threshold.

References

Gardiner C, et al. The effect of caffeine on subsequent sleep: a systematic review and meta-analysis. Sleep Med Rev. 2023;69:101764.

Nehlig A. Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption. Pharmacol Rev. 2018;70(2):384-411.

Low JYQ, et al. Genetic susceptibility to caffeine intake and metabolism: a systematic review. J Transl Med. 2024;22:961.

Ruiz LD, et al. Dose and timing effects of caffeine on subsequent sleep: a randomized clinical crossover trial. Sleep. 2025;48(4):zsae230.