Two settings, and what they start at
Both settings live in Settings, and both offer the same choice: let MiniCycle estimate, or fix a value yourself. Cycle length is the gap from one period start to the next, and by hand you can set it anywhere from 21 to 42 days. Period length is how many days the bleeding lasts, with a manual range of 1 to 10 days.
In automatic mode, the app uses 29 days for cycle length and 5 days for period length only when there are no usable records yet. Those are starting values, not claims about what your cycle should be.
How does the automatic estimate work?
The cycle estimate reads your saved period start dates, up to the latest 12. It measures the gap between each pair of consecutive starts, then takes a median rather than a plain average. A median is the middle value, so one unusual month moves it far less than it would move a mean.
There is one more step once history builds up. When at least 10 measured intervals exist, the app drops the single shortest and the single longest before taking the median. A cycle thrown off by illness, travel, or a missed log stops dragging the estimate around. Period length runs on the same idea: it reads your recent closed period ranges and estimates a typical length, using 5 days only when there is not enough to measure.
Choosing automatic mode
Automatic mode is useful when you regularly log period starts and want the estimate to update from those dates. It uses only the saved history, so a missing or incorrect record can affect the result until you correct it.
Automatic does not mean medically more accurate. It is a median-based summary of recent records, not a measurement of hormones or ovulation.
Choosing a manual value
Manual mode is useful when you have little history in the app but already have a typical value you want the calendar to use. The value remains fixed until you change it, regardless of later records.
A manual number is a preference for the prediction calculation, not a diagnosis or a guarantee. If your pattern is changing or you are unsure which value represents it, keep recording the actual dates and discuss health concerns with a clinician.
What the number changes, and what it leaves alone
Whichever way you set it, the cycle length feeds the forward predictions. Your next expected period is counted from your most recent start using that length. Ovulation is then counted backward from that predicted period using a luteal phase of 9 to 14 days, scaled to your cycle rather than fixed at 14. The fertile window is drawn from 5 days before the estimated ovulation through the day after. Change the cycle length and all of those shift together.
What it does not touch is anything you actually recorded. A period you logged stays on its dates. Period length only shapes how far a new period start is filled in and how the estimate reads your history. It never edits a range you have already closed by hand.
What neither setting can promise
Both modes produce calendar estimates from a chosen or calculated number. They do not detect whether or when ovulation happened, and they cannot explain why a cycle changed.
Treat predicted dates as planning references, not medical advice, contraception, or a way to judge pregnancy. MiniCycle stores records on the device by default; if you enable iCloud Sync, it also stores a copy in your iCloud through Apple CloudKit.
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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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