Pregnancy Due Date
Calculate your pregnancy due date using Naegele's rule. Enter LMP date and cycle length for estimated due date, gestational age, trimester, and pregnancy progress timeline.
About This Calculator
The Pregnancy Due Date Calculator estimates when your baby will arrive using Naegele's rule, the standard medical method for calculating due dates. By entering the first day of your last menstrual period (LMP) and your average cycle length, the calculator provides your estimated due date, current gestational age, trimester information, and a complete pregnancy timeline with progress tracking.
Naegele's rule adds 280 days (40 weeks) to the first day of your LMP, based on a standard 28-day menstrual cycle with ovulation occurring on day 14. For women with longer or shorter cycles, the calculator adjusts accordingly: due date = LMP + 280 days + (cycle length - 28). Conception is estimated at approximately 14 days after LMP, meaning the due date can also be calculated as conception + 266 days (38 weeks). The due month — a four-week window centered on the due date — captures when approximately 80% of babies are born, as only about 5% arrive exactly on the predicted date.
Pregnancy is tracked in three trimesters. The first trimester (weeks 1-12) covers critical organ development. The second trimester (weeks 13-27) involves growth and movement. The third trimester (weeks 28-40) prepares the baby for birth. Regular prenatal care throughout each trimester helps ensure a healthy pregnancy.
Regional Notes
India: Prenatal care typically begins with a confirmation visit between 6-8 weeks. The first ultrasound is usually scheduled between 8-12 weeks. Government schemes like Pradhan Mantri Matru Vandana Yojana provide financial support for pregnant women. Most hospitals offer comprehensive maternity packages.
United States: OB-GYN practices typically schedule the first prenatal visit between 8-10 weeks. Early dating ultrasound is standard. The due date may be adjusted based on ultrasound measurements if there is a significant discrepancy with LMP-based dating. Most insurance plans cover prenatal care.
United Kingdom: The NHS offers a dating scan between 10-14 weeks and a booking appointment with a midwife around 8-10 weeks. Free folic acid and vitamin D supplements are available. Maternity care is provided through midwife-led units or consultant-led care depending on risk factors.
Frequently Asked Questions
How is the due date calculated using Naegele's rule?
Naegele's rule calculates the due date by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). For non-28-day cycles, an adjustment is made: due date = LMP + 280 days + (cycle length - 28 days). This is the standard medical method for estimating due dates.
How accurate is the due date estimate?
The due date is an estimate — only about 4-5% of babies arrive exactly on their calculated due date. Most babies are born within a window of 37 to 42 weeks of pregnancy, which is considered full term. The due month (two weeks before and after the estimated date) captures when about 80% of births occur.
What is the difference between gestational age and fetal age?
Gestational age is measured from the first day of your last menstrual period (LMP) and is about 40 weeks at full term. Fetal age (or conception age) is measured from the actual date of conception, which is about 2 weeks after LMP, making full term about 38 weeks. Healthcare providers use gestational age for all pregnancy dating.
How do pregnancy trimesters work?
Pregnancy is divided into three trimesters. First trimester: weeks 1-12, when the baby's organs and body systems form. Second trimester: weeks 13-27, when the baby grows and you may feel movement. Third trimester: weeks 28-40, when the baby gains weight and the body prepares for birth. Each trimester has specific prenatal care milestones.
When should I schedule my first prenatal appointment?
You should schedule your first prenatal appointment as soon as you confirm pregnancy, ideally around 6-8 weeks gestational age. Early prenatal care allows your provider to confirm the pregnancy, estimate due date, order necessary blood tests, and start essential supplements like folic acid for healthy fetal development.
What if my menstrual cycle is irregular or longer than 28 days?
If your cycle is longer or shorter than 28 days, the due date estimate from LMP alone may be less accurate. Our calculator adjusts for cycle length, but your doctor may use early ultrasound measurements between 8-13 weeks to fine-tune the due date, as ultrasound dating is more reliable with irregular cycles.
What does 'due month' mean and why is it important?
The due month is a two-week window on either side of your estimated due date — about 80% of babies are born within this range. Due date = due date ± 2 weeks. This helps set realistic expectations since only a small percentage of babies arrive exactly on the predicted date.
Can I calculate the due date if I know my conception date?
Yes, if you know your exact conception date, the due date is conception + 266 days (38 weeks). This is equivalent to Naegele's rule minus 14 days. If you track ovulation, you may know your conception date more precisely, which can give a more accurate due date estimate.