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Estimate the caffeine still in your system right now.
☕ Half-life averages ~5 hours but ranges 3-7 (smokers clear faster, oral contraceptives slower). Coffee ≈95 mg/cup, tea ≈47, cola ≈34, energy drinks ≈80-300. Sensitivity varies widely by genetics (CYP1A2).
Caffeine clears exponentially: 200 mg at 3 PM leaves ~100 mg at 8 PM, ~50 mg by 1 AM. That bedtime residue is enough to delay deep sleep even if you fall asleep fine.
The CYP1A2 gene splits people into fast and slow metabolizers. Oral contraceptives roughly double half-life; smoking halves it. Adjust expectations after noticing how late coffee hits you.
Brewed coffee ≈95 mg per cup, espresso ≈63 mg per shot, black tea ≈47 mg, cola ≈34 mg, energy drinks range 80-300 mg, dark chocolate ≈24 mg per 40 g.
Sleep researchers suggest stopping 8-10 hours before bed. For a 10:30 PM sleeper, that means no caffeine after lunch — earlier than most people assume.
Disclaimer: This tool is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Results are estimates and should be discussed with a qualified healthcare provider before making health-related decisions.
The Caffeine Calculator lets you figure out caffeine calculatorinstantly, without reaching for a spreadsheet or doing the math by hand. Whether you're planning a budget, checking a loan, or working through homework, the tool applies the correct formula behind the scenes and shows the result the moment you enter your numbers.
Unlike a static chart or table, this calculator adapts to your exact inputs. You can adjust any value and see the outcome update in real time, which makes it easy to compare scenarios — for example, "what if the rate were 1% lower?" or "what if I paid an extra $50 a month?"
Common uses: people reach for this tool when they need to find a when will coffee wear off calculator, caffeine at 3pm still awake, half life of caffeine 5 hours, or safe caffeine cut off time before bed.
Browser-based tools like this one have a few real advantages over installed software or manual methods:
The Caffeine Calculator is based on the following formula:
C(t) = C₀ × 0.5^(t / H) time to cutoff: t = H × log₂(C₀ / Ccutoff) H ≈ 5-6 hours (population average ≈ 5.7 h)
Variables: C(t) = Caffeine left in the body t hours after a dose (mg) C₀ = Size of the dose consumed (mg) t = Hours since the dose (hours) H = Half-life, about 5-6 hours (average 5.7 h) Ccutoff = Personal cutoff level, e.g. 50-100 mg (mg) log₂ = Base-2 logarithm
Caffeine is eliminated exponentially: each half-life cuts what remains in half, so it never drops to zero abruptly. Every logged drink decays on its own clock, and your current level is the sum of what is left of each one.
Worked example: Step 1: A large coffee = 95 mg at 8:00 am. Step 2: At 2:00 pm (t = 6 h): C = 95 × 0.5^(6/5.7) ≈ 95 × 0.483 ≈ 46 mg. Step 3: At 8:00 pm (t = 12 h): C = 95 × 0.5^(12/5.7) ≈ 95 × 0.232 ≈ 22 mg. Step 4: Time to fall below 50 mg: t = 5.7 × log₂(95/50) ≈ 5.7 × 0.926 ≈ 5.3 h → about 1:17 pm. Result: about 46 mg remains by 2:00 pm and 22 mg by 8:00 pm; you drop under 50 mg around 1:15 pm.
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