Pregnancy Due Date Calculator

The estimated due date is one of the first numbers an obstetrician or midwife calculates. The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle and ovulation on day 14. Actual delivery can vary by two weeks in either direction, so the due date is better thought of as a target window than a precise date. Conception typically occurs around 14 days after the LMP, during ovulation. This calculator shows both the due date and the estimated conception window, which is useful if you are trying to reconcile a positive test result with recent dates or cycle tracking data. The current week of pregnancy counts from the LMP, not from conception. This is why the first two weeks of a 40-week pregnancy technically occur before conception has happened. It is a convention that aligns with how obstetric care is organized rather than a biological statement.

• Planning prenatal appointments: Knowing your due date lets you schedule your first prenatal visit, nuchal translucency scan (weeks 11-13), anatomy scan (weeks 18-20), and glucose screening (weeks 24-28) well in advance.
• Announcing a pregnancy: Many people wait until the second trimester to announce. Knowing which week you are in tells you how far from that milestone you are and helps you time the announcement.
• Coordinating parental leave: HR departments and state leave programs often require a due date estimate weeks or months before delivery. This calculator gives you that number quickly without waiting for a clinical appointment.
• Reconciling a positive test with cycle data: If you track your cycle and have a positive test, the estimated conception date helps you confirm whether the timing aligns with when you believe you ovulated.

• Confusing LMP date with conception date: The calculator asks for the first day of your last menstrual period, not the date you think you conceived. Conception typically happens about 14 days after the LMP, not on the LMP date itself.
• Expecting an exact delivery date: Only about 5% of babies are born on their calculated due date. Full-term delivery occurs any time between 37 and 42 weeks. The due date marks the middle of a normal delivery window.
• Ignoring irregular cycles: Naegele's rule assumes a 28-day cycle. If your cycle is consistently longer or shorter, or irregular, the actual due date may differ from this estimate by one to two weeks. An early ultrasound provides a more individualized date.
• Using the conception date as the start of pregnancy: Obstetric weeks count from the LMP, not from conception. Week one of pregnancy begins on the LMP date. This is a clinical convention, but it means gestational age is always about two weeks more than time since conception.

1. 1Enter the date your last menstrual period began. If you are unsure of the exact day, use the first day of your most recent period.
2. 2Choose whether you want to find the due date or see your current week of pregnancy.
3. 3The calculator adds 280 days to the LMP to compute the estimated due date (Naegele's rule).
4. 4It adds 14 days to the LMP to estimate the conception window, based on a standard 28-day cycle.
5. 5It divides the number of days since the LMP by 7 to find weeks pregnant, with any remaining days shown separately.
6. 6It assigns a trimester: first (weeks 1-12), second (weeks 13-27), and third (week 28 onward).

• Record your LMP in a note app as soon as your period starts: If you later need to calculate a due date or confirm a positive test, having the exact LMP date saves time and removes guesswork. A note with the date takes seconds to save.
• Use the result as an estimate, not a deadline: Plan for delivery two weeks before and two weeks after the calculated due date. Arranging childcare, travel, and work leave around a two-week window is more realistic than planning for a single day.
• Ask about early ultrasound if your cycle is irregular: An ultrasound before 10 weeks measures crown-rump length and gives an accurate gestational age regardless of cycle length. If your cycles vary by more than a few days, request early dating.
• Check trimester timing before scheduling optional tests: Several screening tests have narrow timing windows. The NIPT blood test is typically offered from week 10, nuchal translucency from 11-13 weeks, and anatomy scan from 18-20 weeks. Knowing your current week helps you schedule on time.