Your first period date is the anchor for everything else — phases, cycle day, and predictions all calculate from it.
Pick the start date of your most recent period. If you're mid-cycle and unsure, an approximate date is fine — you can correct it later and the app recalculates.
During profile setup you can enter a date manually or choose Import from Apple Health on the same screen.
From onboarding
01
Enter Manually
After Birthday in profile setup, choose Enter Manually to pick your last period start date on the calendar.
02
Calendar
Tap the first day your last period began on the calendar below. Colored phase dots appear around your selection as you pick a date.
03
Continue
Tap Continue once a date is selected. The app creates your first cycle with default phases.
Already finished onboarding? Jump here.
Later, from Home
01
Center +
Tap the center + on the tab bar to open the add log options sheet.
02
Track Period
Select Track Period to open the period calendar.
01
Calendar
Tap the first day your period started. Phase-colored dots preview your selection before you save. Future dates are not allowed in this mode.
02
Save
After a valid date is selected, tap Save. A Saved! confirmation appears. Cancel or Done rolls back unsaved preview changes.
✦Period and cycle data stay on your device and sync through your private iCloud—they are not stored on Red Tent servers. Optional research data sharing is separate and revocable anytime in Settings. Logging at least two periods sharpens predictions a lot — the app learns your cycle length.