Kaff — Caffeine Watch

Kaff estimates how much caffeine is still in your body and shows it on your Apple Watch face. You log what you drink: an espresso, a tea, a cola, or an amount in milligrams. You set the volume with the Digital Crown. If you forgot a drink, you can add it later, up to 24 hours back. Kaff then works out, minute by minute, how much is left. It uses the standard pharmacokinetic model for caffeine: the level rises for about 45 minutes, then falls according to your half-life, which you can set from 2 to 10 hours. The main screen shows: • the current amount, compared with the peak of a 200 mg dose; • today's total, compared with the 400 mg a day recommended by EFSA; • what will be left at bedtime, and when you will drop below 35 mg. The complication shows the level on your watch face and keeps it up to date on its own, without opening the app. Optionally, Kaff can work out your usual bedtime from the nights recorded in Health. It can also let you know when your level has come down, or when one more coffee would likely affect your sleep. Entries are saved to the Health app. Kaff has no account, no ads and no server: none of your data leaves your watch. The limits come from EFSA, the FDA and a 2023 meta-analysis on caffeine and sleep. Every source can be viewed in the app. Kaff gives an estimate, not medical advice. No sensor measures caffeine: the calculation relies on what you enter, and the real caffeine content of a cup varies a lot from one coffee shop to another. For adults only; not suitable during pregnancy.