It estimates your fertile window and ovulation day based on the average length of your menstrual cycle and the start date of your last period.
A common method is Naegele’s Rule: Estimated Due Date = First day of last menstrual period + 280 days (40 weeks).
No. They are estimates. Cycle variability, irregular periods, and conception timing affect accuracy; ultrasound provides more precise dating.
Some calculators accept average cycle length and variability; for highly irregular cycles, consult a healthcare provider for tailored guidance.
Not always. In a typical 28-day cycle ovulation is around day 14, but it shifts with longer or shorter cycles.