Coffee & Caffeine Calculator
Calculate total caffeine intake, safe daily limits, and how long until caffeine leaves your system.
To estimate current caffeine in your system
How to Use
1. Enter your body weight 2. Select your drinks and quantities for the day 3. Enter how many hours ago you had your last caffeineSafe limits (general guidance):
Formula
Caffeine Remaining = Total × (0.5)^(Hours / Half-Life) | Half-Life ≈ 5 hoursFrequently Asked Questions
Why does coffee affect me differently to others?
Caffeine metabolism is largely genetic. The CYP1A2 gene determines your rate — fast metabolisers clear caffeine quickly, slow metabolisers feel effects for much longer.
What is the half-life of caffeine?
Approximately 5 hours for most adults. This means 5 hours after 200mg, ~100mg remains. 10 hours later, ~50mg. It takes about 25 hours to fully clear 200mg.
Does caffeine affect sleep?
Yes — caffeine blocks adenosine receptors that promote sleep. With a 5hr half-life, a 200mg coffee at 3pm leaves ~100mg in your system at 8pm, which can delay sleep onset and reduce deep sleep.
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