28-day cycle
- Input
- DUM: 1º de janeiro · Ciclo: 28 dias
- Expected output
- DPP: 7 de outubro
Standard case, aligns perfectly with Naegele's Rule.
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how to calculate due date naegele rule
Naegele's Rule adds 280 days (40 weeks) to the last menstrual period date to estimate delivery. This page explains the logic, assumptions and limitations of the calculation. The calculator applies that sum literally, taking the entered LMP and adding exactly 280 calendar days, with no automatic adjustment for the actual length of the menstrual cycle. LMP dates older than 294 days (42 weeks) are rejected by the tool, since they no longer represent an ongoing pregnancy, and the field also rejects a future LMP, since a pregnancy cannot be dated from a day that has not yet happened.
Standard case, aligns perfectly with Naegele's Rule.
Ovulation occurs on day 21, not day 14, the real due date is shifted forward.
Ovulation occurs on day 7, not day 14, the real due date is shifted backward.
Naegele's Rule adds 280 days (40 weeks) to the last menstrual period date to estimate the due date. It assumes a 28-day cycle and ovulation on day 14. Longer or shorter cycles shift the actual time of ovulation, which is why ultrasound is more accurate for confirming or revising the individual EDD.
No. Only about 5% of births happen on the exact EDD. Most occur within a two-week window before or after.
Yes. If the difference between the LMP-based EDD and ultrasound measurements is relevant, ACOG recommends adjusting the EDD.
Because Naegele's Rule, as implemented here, always adds a fixed 280 days to the LMP. There is no cycle-length field because the calculation does not use that data, it is a population-level approximation, not an individualized formula. To factor in cycle length, use the fertile window calculator, which does accept it.
Medical notice: this calculation is educational, based on population-level averages, and does not replace prenatal care, ultrasound, diagnosis or guidance from a doctor or obstetrician.
The date you enter stays in your browser only. We do not save or send this data.