How estimates work.

With little or no history, Dela uses the cycle length the person reported and shows wider uncertainty.

Every cycle you log teaches Dela more about your pattern, and estimates typically sharpen as your history grows. The displayed range narrows when your recorded cycles run steady, and widens when history is sparse, variable or marked irregular. Real life still moves timing: illness, stress, medication, postpartum changes, perimenopause, hormonal contraception and ordinary biological variation can all shift a cycle.

Fertile timing based only on a calendar is derived from an estimated ovulation day, not measured ovulation.

Logged signs

Logged cervical fluid and ovulation test results can add context about possible timing.

Temperature

A sustained shift in basal temperature is retrospective evidence only: it can suggest that ovulation may already have occurred, but temperature alone does not prove an exact day. Fever, sleep disruption, alcohol, travel, measurement time, and device differences can affect readings.

Dela pauses natural fertile window and ovulation estimates when pregnancy is active or when an active hormonal method makes the assumption about a natural cycle inappropriate. If Dela cannot identify the active method, it does not show those estimates.

If a person enters a due date from a clinician, Dela uses that date for its week counter.

Otherwise, the general fallback adds 280 days to the first day of the entered last menstrual period. This does not account for every cycle pattern, assisted reproduction date, or ultrasound finding. A clinician's obstetric estimate should replace an app estimate; an ultrasound in the first trimester is generally more accurate for clinical dating.