Cycles

LAPLACE Cycles dynamically calculates cycle predictions from the periods you log for each profile. Estimates are recomputed in real time whenever they are displayed. They are never permanently stored in your database and never convert into period logs—only dates you explicitly record are treated as confirmed entries.

Cycle Phases

Profiles without any recorded periods display “Log a period to see predictions.”

On a profile card and in the calendar day details, confirmed bleeding days are marked as Logged Period, while projected dates are labeled Estimated Phase or Rough Estimate. Tap any phase badge to open About This Period or About This Estimate for detailed context.

Cycle Length

1. Overlapping or contiguous period logs are automatically merged and counted as a single period.
2. The app evaluates up to eight recent intervals between consecutive period start dates, filtering out outlier intervals shorter than 15 days or longer than 60 days.
3. The shortest of these intervals serves as an anchor, bounded between 80% of the profile's Typical Cycle and that value plus 10 days. Any interval equal to or exceeding 1.6 times this anchor is treated as a probable missed log and excluded from calculations.
4. If there are only one or two valid intervals and each is at least 1.6 times the profile's Typical Cycle, no shorter interval is available as an anchor. Each interval then counts as the nearest whole number of Typical Cycle lengths, and the prediction is likewise marked as a rough estimate. A third such interval is taken as a pattern of long cycles; setting Typical Cycle closer to these intervals also lets them count at their actual length.
5. The estimated cycle length is the median of the remaining valid intervals. If no eligible intervals exist (for example, when only one period has been logged), the profile's configured Typical Cycle is used instead.

This is a conservative approach: a long gap doesn't prove that a period occurred in between.

Period duration is calculated as the median of the six most recent logged durations. In the absence of multiple intervals, the app selects the greater of the recorded duration and the profile's Typical Period, ensuring that a first period currently underway is not cut short prematurely.

Ovulation Window

Ovulation is estimated to occur 14 days before the start of the next predicted period. The Estimated Ovulation Window spans five days before through one day after that estimated ovulation date. The window is bounded so that it never overlaps with an active period or extends into the following cycle. Profile screens also display the calculation basis, such as “Based on a 28-day cycle”.

Rough Estimates

Under certain conditions, upcoming periods and ovulation windows appear in faded colors and are labeled Rough Estimate:

• Limited history: Only a single period has been recorded, meaning a true cycle interval cannot yet be calculated.
• Varying cycles or a possible gap: The difference between the longest and shortest valid intervals exceeds seven days, or an interval was excluded or adjusted for being unusually short, long, or likely skipping a cycle.
• The latest period may be missing: The predicted period date has arrived without a new log. Subsequent dates project future cycles in faded tones as ongoing estimates, never converting into confirmed logs.

Even when a current period is actively logged, upcoming periods and ovulation windows remain faded if overall cycle predictions remain uncertain.

Compared with Estimates

Each logged cycle is compared with the length estimated on its first day: the app replays that day's prediction from only the periods logged by then, using today's method and Typical Cycle. The Cycle History chart marks each finished cycle's estimate and, once two cycles can be compared, shows the average difference.

• Cycles outside the plausible range (15–60 days) or at least 1.6 times their estimate aren't compared, so a likely missed log doesn't count as a late period, though a genuinely long cycle is left out too
• The difference is how many days the next period started from its estimated date. It says nothing about ovulation, which the app never observes
• Like other predictions, these estimates are calculated from period logs when needed and never stored

Dates and Time Zones

Each period log preserves the original time zone in which it was recorded. For example, an entry logged on September 1 remains anchored to September 1 when traveling abroad or viewing it on a synced device in another time zone. Day counts follow local calendar dates and are unaffected by daylight saving time shifts.

When viewing past dates, calculations only consider logs that began on or before that specific date. When viewing future dates, estimates reflect what is known as of today—an upcoming period is never flagged as missed before its predicted date has actually passed.

Learn More

Under Settings > How Predictions Work, tap Learn About the Menstrual Cycle to read the comprehensive guide provided by the U.S. Department of Health and Human Services Office on Women's Health.