Put the next day in context

What changes after a few drinks, or more? KATER ZERRO compares days after drinking with your own alcohol-free days, using Apple Health data you choose to share.

Sleep, resting heart rate and heart-rate variability are grouped by the drinks logged the previous day. This makes personal patterns easier to spot.

Alcohol-free days form the reference. A bar above or below the line shows a difference from your baseline; it does not prove alcohol caused it or label one direction as better for every metric.

More recorded days and measurements make comparison more useful. When data or a permission is missing, the app says so plainly instead of treating a thin data set as an answer.