🧘 Caffeine Half-Life Calculator

Caffeine's half-life in healthy adults averages 5–6 hours, but ranges from 1.5 to 9.5 hours depending on genetics (CYP1A2 enzyme variation), smoking status, pregnancy, liver function, and certain medications. Oral contraceptives roughly double caffeine half-life.

Enter the dose, time consumed, and your metaboliser type. The calculator models exponential decay using your half-life estimate to show how much caffeine remains in your bloodstream over time. This helps identify your optimal caffeine cut-off time to protect sleep.

Research shows caffeine levels above ~100mg in your system at bedtime meaningfully delay sleep onset and reduce slow-wave (deep) sleep. This means a typical 200mg coffee consumed 6 hours before bed still leaves ~100mg in a slow metaboliser's blood.

Caffeine blocks adenosine receptors rather than eliminating adenosine. Sleep pressure (adenosine) continues building while blocked. When caffeine wears off, accumulated adenosine floods receptors causing a crash. Meanwhile, caffeine-disrupted sleep architecture reduces restoration even when sleep quantity is maintained.

Fast metabolisers carry the CYP1A2*1F genetic variant and clear caffeine roughly 40% faster than slow metabolisers. Fast metabolisers have a half-life of ~3–4 hours; slow metabolisers 6–9 hours. A DNA test (23andMe or similar) can identify your type.

For an average 5-hour half-life metaboliser: last caffeine by 2–3pm to keep bedtime levels under 50mg. For a slow metaboliser (7-hour half-life): noon is safer. For a fast metaboliser: a 4–5pm cut-off may suffice.

Approximate caffeine: espresso 63mg/shot, drip coffee 95mg/cup, cold brew 100–200mg, energy drink 80–150mg, black tea 47mg, green tea 28mg, matcha 70mg, dark chocolate bar 20mg. Levels vary significantly between brands and brew methods.

Yes. Caffeine increases cortisol and adrenaline, and at doses above ~300mg can cause palpitations, jitteriness, and anxiety — particularly in slow metabolisers and people with anxiety disorders. Those with generalised anxiety disorder are advised to minimise or avoid caffeine.

Yes. Regular caffeine use downregulates adenosine receptors, requiring larger doses to achieve the same alertness effect. However, tolerance to caffeine's sleep-disrupting effects is incomplete — even habitual users show measurable sleep architecture disruption from evening caffeine.

Adenosine receptor upregulation from habitual caffeine use reverses within 7–10 days of abstinence. Withdrawal symptoms (headache, fatigue, irritability) peak at 20–51 hours and resolve within 2–9 days. Tapering by 10% per day minimises withdrawal symptoms.