Where the setting lives, and what it changes
Open Settings, find Week starts on, and pick Sunday or Monday. MiniCycle starts with Sunday selected on a new install.
Choosing Monday moves Monday to the first column and places Saturday and Sunday at the right side of each row. This is a display preference; it does not alter a date or its weekday.
Why calendars disagree
The first day of the week is a convention rather than a property of time. ISO 8601 uses Monday, while regional calendar conventions vary.
Unicode CLDR publishes locale data that software can use for regional week settings. MiniCycle does not automatically follow that locale value; it provides its own Sunday-or-Monday control so you can choose the layout you prefer.
Does changing the week start move my periods?
No, and this part is worth saying plainly. A period you logged on the 14th stays on the 14th. The cycle math, your next expected period, the ovulation estimate, and the fertile window all run on dates, not on which column a date happens to sit in. Switching from Sunday to Monday reflows the grid and changes nothing you recorded or predicted.
So the reason to choose is readability, not accuracy. If you treat the weekend as the end of the week, a Monday start keeps Saturday and Sunday together at the right. If you grew up scanning Sunday-first calendars, that layout will read faster for you. Pick the arrangement your eyes already expect, and the month gets quicker to read.
Why the widget uses the same setting
The home-screen widget reads the same saved week-start preference as the app, so both grids use the same first column.
Changing the setting asks WidgetKit for a new timeline, but iOS decides when the widget redraws. The old layout may remain briefly even after you open the app.
What the week start cannot change
This is a layout preference, so its reach ends at layout. It will not make a 31-day month shorter, change which weekday a date falls on, or move an estimate by a single day. Those come from your records and the cycle calculation, and this setting touches neither.
Like every date in MiniCycle, the calendar is reference information for planning, not medical advice, contraception, or a way to judge pregnancy. The week start only decides how that information is arranged on screen. If the grid has never quite matched the way you read a week, the fix is one tap in Settings.
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MiniCycle is built for a clean iPhone period calendar, local records, simple statistics, and a home screen widget.
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