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Caffeine Half-Life Calculator

Model how caffeine from your coffee, tea or energy drink decays over the next 12 hours and see how much is likely left when you go to bed.

Based on the average adult caffeine half-life of about 5 hours — every 5 hours, roughly half of what remains clears from your system.

The 5-hour half-life is an average for healthy adults and varies a lot by person — pregnancy, liver conditions and some medications can slow it significantly, while regular smoking tends to speed it up. This is general information, not medical advice.

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Reading dose and timing
Modeling the decay curve
Checking your bedtime level

Result

Caffeine does not just wear off — it decays on a curve, and this calculator draws that curve for you. Pick a drink (or enter a custom milligram dose), the time you drank it and your usual bedtime, and it models how much caffeine is mathematically likely to remain in your bloodstream every hour for the next 12 hours.

The model uses the commonly cited average elimination half-life for a healthy adult, about 5 hours: every 5 hours, roughly half of the remaining caffeine clears. That means a 95 mg cup of coffee leaves about 47 mg after 5 hours, 24 mg after 10 hours, and so on — a slow tail that is easy to underestimate, especially for drinks had in the afternoon or evening.

The half-life of 5 hours is a population average, not a personal fact. It varies significantly from person to person and can run notably longer during pregnancy, with certain liver conditions, or with some medications, and notably shorter for regular smokers, who metabolize caffeine faster. This tool models the average case — it is general information, not medical advice, and it cannot account for your specific physiology.

The headline result is deliberately practical: exactly how many milligrams are likely still active when you plan to fall asleep, so you can decide for yourself whether that afternoon espresso or evening energy drink is worth the wired 2 am. Pair it with our sleep calculator to plan bedtime and wake windows around what you learn here.

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Accepted Formats & Rules

  • Preset doses: espresso (~63 mg), drip coffee (~95 mg), energy drink (~160 mg), black tea (~47 mg), plus a custom milligram field.
  • Time-consumed and bedtime inputs, with the consumed time defaulting to right now.
  • Bedtime callout: 'approximately X mg will likely still be in your system' as the key takeaway.
  • Hour-by-hour decay bars for 12 hours after the drink, with a copyable text summary.

Key Benefits

✓ Built-in doses for espresso, drip coffee, energy drinks and black tea, or enter any custom milligram amount.
✓ The single most useful number up front: approximately how many milligrams will likely still be in your system at your own bedtime.
✓ A full 12-hour decay curve, hour by hour, so you can see exactly when caffeine drops below a level that matters to you.
✓ Everything is computed locally in your browser from the average adult half-life — no data ever leaves your device.

Use Cases

  • • Check whether that 4 pm energy drink will still be active at your bedtime, and by roughly how many milligrams.
  • • Plan a caffeine cutoff time backward from a fixed bedtime, comparing espresso, coffee and tea doses side by side.
  • • See the full 12-hour decay curve after a custom dose to judge when caffeine drops to a level that stops mattering for sleep.