Reading estimates
lunarlog's estimate is the average of recent cycle lengths counted forward from the last logged period start — an honest guess from your own history, and nothing more. It comes with labels that say how much to trust it. Estimates only — never medical advice.
What the estimate is
What the next-period estimate is
The average of recent cycle lengths added to the last period start. An average, not a promise.
The app takes the most recent usable cycle lengths, averages them, and counts that many days forward from the last logged period start. That date is the estimate.
When recent cycles differ from each other, the app shows a range (a few days either side of the estimate) instead of one exact date. Wider spread means a wider range.
Logging more cycles sharpens the average. Skipped or unusual cycles can be left out of the average from the history list without deleting them.
Estimates only — not medical advice.
Source: lunarlog's own prediction model · Last reviewed
Why a new profile has no estimate
The app waits for three completed cycles before it estimates anything. Until then it says so plainly instead of guessing — Why three completed cycles? is a link, not an error, and the calendar caption reads No estimates yet — keep logging. Estimated bands appear on the calendar once a few cycles are recorded..
Why no estimate yet?
The app waits for three completed cycles before it estimates anything. This is working as intended.
A period estimate is an average of past cycle lengths. With fewer than three completed cycles there is nothing honest to average, so the app shows "not enough history yet" instead of guessing.
A cycle counts as completed once a new period starts after the last one, so the cycle you are in right now does not count yet. Cycles shorter than 15 days or longer than 60 days stay in history but never feed the average, because they would pull it away from the usual pattern.
Keep logging period starts. The estimate appears on its own once three completed cycles are recorded — usually around three months of logging.
Estimates only — not medical advice. If something worries you, talk to a doctor or another clinician you trust.
Source: lunarlog's own prediction model · Last reviewed
The confidence labels
Every estimate carries one of four labels, and the app summarizes each in place. The labels in the app's own words:
- High confidence — Recent cycles are steady — estimates are at their most reliable.
- Learning — Still learning — estimates improve after a few more cycles.
- Irregular — Cycles vary a lot — treat estimates as rough guides.
- Provisional — Based on your onboarding answers — estimates improve once real cycles are logged.
What the confidence label means
High, Learning, Irregular, and Provisional say how steady the logged history behind an estimate is.
High means recent cycles are steady, so the estimate is at its most reliable. Learning means there are only a few usable cycles so far — the estimate improves as more are logged.
Irregular means logged cycles vary a lot, so the estimate is a rough guide. A range is shown instead of a single date whenever the label is not High.
Provisional means the estimate comes from onboarding answers, not logged cycles yet. It is replaced by a computed estimate once three real cycles are recorded.
Estimates only — not medical advice.
Source: lunarlog's own prediction model · Last reviewed
The label matters more than the date: whenever the estimate is not High confidence, the app shows a range of likely days rather than one exact date, and the wider the history spreads, the wider the range.
Irregular cycles
For cycles that simply vary — a teenager's first years, or perimenopause — profiles can carry the Irregular cycles framing:
Treats variation as expected, not late: ranges instead of dates, no late banner, no late nudges. On by default for teen profiles until cycles are steady.
It is a framing switch, not a separate engine: the same honest maths, presented as ranges instead of dates, with no late banner and no late nudges. Teen care mode turns it on by default until cycles steady, and it can be changed any time from Edit profile.
When the estimate passes
A few days past the estimated date, the app asks what to do rather than nagging. It offers three options, in the app's words: Log it, Skip this cycle, or Remind me in 3 days. Logging the period closes the cycle and everything recomputes; skipping leaves the cycle in history but out of the average.
Why the app says a period is late
"Late" only means today is past the estimated date. The estimate is an average, and averages miss. Teen-mode profiles never see the "late" wording.
The app compares today with the estimated next start. A few days past it, the resolver offers three options: log the period, skip this cycle, or be reminded again in three days.
Logging the period closes the cycle and the whole estimate recomputes. Skipping leaves the cycle in history but out of the average, and moves the estimate one average cycle later.
In the first few years after periods start — and at other times, like perimenopause — cycle lengths vary naturally, and an estimate built on averages will miss more often. That is variation, not a fault. Profiles set to the teen care mode never see this banner: a teen’s cycles are still settling, and "late" can read as a failure when nothing is wrong, so those profiles get a quiet "log it when it comes" line instead.
The "irregular cycles" framing switch is a separate setting. It changes how much the estimate hedges, but it is not what keeps this banner away from a teen — teen mode does that on its own, at every stage.
A late estimate is only about the maths — the lateness itself is not a sign that anything is wrong, but it does not rule anything out. If something worries you, talk to a doctor or another clinician you trust.
If there’s any chance of pregnancy, take a pregnancy test. With a copper IUD, a missed period is a reason to contact a clinician.
Estimates only — not medical advice.
Source: ACOG Committee Opinion 651; ACOG FAQ047 · Last reviewed
And the "late" in that card carries the important caveat: the estimate is an average, and averages miss. A late estimate is arithmetic, not a diagnosis — the card routes worry to a clinician, and so does this guide.
Skipping a cycle in the average
An unusual cycle can be left out of the average without deleting it. History stays complete; the maths stays honest.
"Skip this cycle" marks the open cycle’s start as omitted. The estimate advances one average cycle, and when the next period is logged, that cycle’s real length never feeds the mean.
Omitted cycles stay visible in history. The omission can be undone from the history list, which puts the cycle back into the average.
Use this for cycles you know were unusual — for example after illness, travel, or a missed log — rather than deleting entries.
Source: lunarlog app behaviour · Last reviewed
Turning estimates off
Estimates are a feature, not an obligation. A profile can turn them off — Show estimates in Settings — and keep tracking with no dates predicted at all. When cycles vary widely, the app itself may suggest exactly that.