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Frequently asked

• How is the bedtime projection calculated?+

  cafein uses a bi-exponential pharmacokinetics model. Caffeine is absorbed over about 30 minutes after a drink, then decays exponentially with a default half-life of 5 hours. The projection extrapolates from every cup you have logged today and shows the projected level at your set bedtime.

• What is the cortisol "good window"?+

  When you wake up, your body produces a natural surge of cortisol that keeps you alert for about the first hour. Drinking coffee during that surge is wasted — your body already has a stimulant on tap. cafein highlights the window after the cortisol peak (typically 1.5 to 3.5 hours after waking) where caffeine has the biggest measurable effect.

• How does Apple Health sync work?+

  Every coffee you log writes to Apple Health as caffeine intake (mg). cafein also reads Apple Health, so coffees you log from Siri shortcuts, your watch, or other apps appear in cafein. You can toggle the sync on or off in Settings any time.

• Can I export my data?+

  Yes. cafein Pro includes a CSV export designed for AI assistants — you can drop the file into ChatGPT, Gemini, or Claude and ask things like "what time of day do my biggest coffees usually happen?" Free users have full access to their data through Apple Health.

• Is there an Android version?+

  Not yet. We are iOS-first because of the depth of Apple Health integration. Android with Health Connect support is on the roadmap.

• How do I cancel my cafein Pro subscription?+

  Subscriptions are managed by Apple. Open the Settings app on your iPhone, tap your name at the top, then "Subscriptions", find cafein, and choose Cancel. Your Pro features stay active until the end of the current billing period.

• Can I customize my caffeine half-life?+

  Yes. The default is 5 hours, which is the population average, but caffeine clearance varies by 2 to 10x between individuals. If you know yours (some people do, after experimenting), or if cafein consistently over- or under-predicts, you can adjust it in Settings.

• I logged a coffee but the chart shows nothing.+

  cafein backdates each log by 15 minutes (because most people tap "Save" after they have already started drinking). If your log is very recent, the curve may not have visibly risen yet. Wait a couple of minutes and it should appear.

• My subscription does not show as active.+

  Open Settings inside cafein and tap "Restore purchases". This re-syncs with Apple. If it still does not show, email us — we can confirm the purchase from the receipt.

• Does cafein give medical advice?+

  No. cafein is an educational and tracking tool. It is not a diagnostic device, and it does not replace medical advice. If caffeine is interfering with your sleep or health in a serious way, talk to your doctor.