Caffeine calculator for coffee timing and sleep

It is a practical estimate, not a lab measurement. The caffeine content of coffee varies significantly based on bean origin, grind size, water temperature, and extraction time. The half-life of caffeine also varies widely between people, from under 2 hours to over 9 hours, depending on genetics, medications, pregnancy, and liver health. Use the results as an informed guide, not a precise number.

Research from EFSA (2015) and the NIH puts the average caffeine half-life in healthy, non-pregnant adults at approximately 4–5 hours, with a range of roughly 1.5 to 9.5 hours (Frontiers in Pharmacology, 2021). At a 5-hour half-life: 200 mg at noon leaves ~100 mg at 5 pm and ~50 mg at 10 pm. Factors like pregnancy (can triple the half-life), oral contraceptives (roughly double it), smoking (reduces it by 30–50%), and certain medications can dramatically shift your personal clearance rate.

The landmark study by Drake et al. (Journal of Clinical Sleep Medicine, 2013) found that 400 mg of caffeine consumed even 6 hours before bedtime reduced total sleep time by more than an hour, even when participants did not feel the effect. A 2024 randomized trial in the journal SLEEP found that a standard cup of coffee needed to be consumed at least 8.8 hours before bedtime to avoid measurable sleep disruption. A general safe rule: cut off caffeine at least 6 to 8 hours before you plan to sleep.

The European Food Safety Authority (EFSA, 2015) and the FDA both put the safe limit for healthy adults at 400 mg per day, roughly 4 cups of filter coffee. Single doses up to 200 mg are generally considered safe. For pregnant women, EFSA recommends staying under 200 mg per day. These are population-level guidelines; individuals with certain health conditions, medications, or genetic slow-metabolizer status may need to set a lower personal limit.

Roughly 95% of caffeine is metabolized by the CYP1A2 liver enzyme, which is largely controlled by genetics. The CYP1A2 gene variant rs762551 splits the population into fast metabolizers (AA genotype) and slow metabolizers (CC genotype). A landmark JAMA study (Cornelis et al., 2006) found that slow metabolizers who drank more than 4 cups per day had a 63% higher risk of heart attack compared to light consumers, while fast metabolizers showed no such association. Smoking strongly induces CYP1A2 (speeds caffeine clearance); pregnancy, oral contraceptives, and certain medications inhibit it (slows clearance).

Barely, when measured by weight. Light roast beans are denser, so a gram of light roast contains slightly more caffeine than a gram of dark roast, roughly a 3 to 5 percent difference. Brew method and dose have a much larger effect on total caffeine yield.

A standard double espresso (18 g in / 36 g out) contains approximately 120 to 130 mg of caffeine. An 8 oz cup of drip or pour-over coffee typically contains 90 to 165 mg, often more than a double espresso despite being less concentrated, simply because of the larger serving volume. Cold brew concentrate can deliver 150 to 240 mg per 8 oz before dilution. (Source: USDA FoodData Central; University of Newcastle, 2018.)

Not significantly. Beyond a reasonable brew ratio, adding more water dilutes the cup rather than extracting more caffeine. The tool applies a small extraction factor based on your brew ratio, reflecting that under-extracted coffee (very low water) can under-deliver caffeine, but the effect is modest compared to your dose (grams of coffee).