Due Date Calculator

Enter the first day of your last menstrual period (LMP) and, if known, your actual cycle length. This tool uses Naegele's rule to compute your due date, current gestational age, and a full prenatal checkup schedule.

How to use

Select the first day of your last menstrual period.
If your cycles are regular, enter your typical cycle length.
Submit to see your due date, current gestational age, and prenatal schedule.

How the calculation works

Naegele's rule: due date = LMP + 280 days (adjusted for actual cycle length: due = LMP + 280 + (cycle − 28)). Roughly 5% of babies are born on the exact due date — normal birth is between 37 and 41 weeks.

FAQ

Does the due date tell me exactly when I will give birth?

No. It is the statistical 40-week mark. Normal delivery occurs anywhere between 37 and 41 weeks; only about 5% of babies are born on the exact due date.

What if my cycles are irregular?

Naegele's rule is less reliable for irregular cycles. In early pregnancy (7–12 weeks), ultrasound dating is more accurate — always follow your doctor's dating.

Why does my ultrasound say a different number of weeks?

That is normal. Early ultrasound (crown-rump length at 7–12 weeks) is usually more accurate than LMP-based dating. When the two differ, the doctor's ultrasound-based date takes priority.

References

Naegele's rule (obstetric standard of care)
WHO — Antenatal care recommendations (https://www.who.int/teams/reproductive-health/maternal-care/antenatal-care)

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