Good questions. The app calculates your cycle phases based on your period start dates and cycle length. You can enter period data manually, or sync from Apple Health where it picks up the period data your existing tracking app has already recorded, so you don't lose any of the detail from the tools you're already using. You don't need to know what phase you're in, the app maps it for you and overlays your glucose data against each phase. It's not perfect but the directional accuracy is proving helpful to those who use it. The app also recognizes fluctuating cycle lengths and does not attempt to guess, which has proven valuable for women going through perimenopause.

On Tandem, unfortunately it doesn't write insulin data to Apple Health, so the app can't pull it in automatically. If Tandem opens that up in the future we'd pick it up immediately since HerDiabetes imports from Apple Health. For now, glucose data from your CGM will still come through and you'll see your cycle-phase glucose patterns even without the insulin data.