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Coffee 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

This page opens the caffeine half-life calculator preloaded with a standard drip coffee dose — about 95 mg, roughly what an 8 oz cup delivers — and computes the decay curve as soon as it loads.

At the average adult half-life of about 5 hours, a coffee drunk at 8 am still has roughly 24 mg circulating by 6 pm, and around 12 mg left by 11 pm. That is enough for some people to notice trouble falling asleep, which is why the calculator asks for your own bedtime rather than assuming one.

Adjust the time you drank it and your bedtime above to get your personal number, or switch the drink selector to model an espresso, an energy drink or a custom dose instead.

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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.