Pregnancy Due Date Calculator
Enter the first day of your last menstrual period to calculate your estimated due date and trimester milestones.
Pregnancy Milestone Timeline
| Milestone | Week | Notes |
|---|---|---|
| Positive pregnancy test | 4–5 | hCG detectable |
| First prenatal visit | 8–10 | Heartbeat confirmed |
| End of 1st trimester | 13 | Miscarriage risk drops |
| Anatomy scan (ultrasound) | 18–20 | Gender often visible |
| Glucose test | 24–28 | Gestational diabetes screening |
| End of 2nd trimester | 27 | Baby viable outside womb |
| Group B Strep test | 35–37 | Routine prenatal test |
| Full term | 39–40 | Optimal birth window |
General reference only. Always follow your healthcare provider's specific guidance and schedule.
Frequently Asked Questions
How is the due date calculated?
The most common method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. Your healthcare provider may adjust the due date based on first-trimester ultrasound measurements, which are the most accurate. Only about 5% of babies are born on their exact due date — most arrive within 2 weeks before or after.
What are the three trimesters of pregnancy?
Pregnancy is divided into three trimesters: First trimester (weeks 1–13): organ formation, highest miscarriage risk, morning sickness common. Second trimester (weeks 14–27): typically the most comfortable, baby grows rapidly, anatomy scan around week 20. Third trimester (weeks 28–40+): baby gains weight, lungs mature, prepares for birth. 'Full term' is defined as 39–40 weeks; babies born at 37–38 weeks are 'early term,' before 37 weeks is 'preterm.'
How accurate is the LMP due date calculation?
The LMP-based due date is accurate for women with regular 28-day cycles. For longer or shorter cycles, the date may be off by several days. First-trimester ultrasound (7–10 weeks) is the most accurate dating method, with a margin of error of ±5–7 days. Second-trimester ultrasound (18–22 weeks) has a wider margin of ±2 weeks. Your OB will establish your official due date based on the most accurate available data, typically the first ultrasound.
What is the difference between gestational age and fetal age?
Gestational age is counted from the first day of your last menstrual period — this is the standard medical measurement. Fetal age (or embryonic age) counts from conception, which is approximately 2 weeks after LMP. A 10-week-old baby by gestational age is 8 weeks by fetal age. Medical providers always use gestational age. When your doctor says you are '10 weeks pregnant,' they mean 10 weeks since your LMP, not 10 weeks since conception.