Put the next day in context

What changes for you after a couple of drinks, and what changes after more? KATER ZERRO compares the days after drinking with your own alcohol-free days, using the Apple Health information you have chosen to share.

Sleep, resting heart rate, heart-rate variability and other available signals are grouped by the amount you logged during the previous drinking day. That makes it possible to look at patterns across your own history rather than someone else’s average.

The alcohol-free days form the personal reference. A bar above or below that line shows a difference from your baseline; it does not claim that alcohol caused it, or that one direction is automatically better for every metric.

More recorded days and measurements make the comparison more useful. If a permission or enough data is missing, the app says so plainly instead of pretending a thin data set can answer more than it can.