About Pregnancy Due Date Calculator
Calculate your pregnancy due date, current week, and trimester milestones. Enter your last menstrual period or conception date to track your full pregnancy timeline. Free.
How to use
- Choose your calculation method: Last Menstrual Period (LMP) or conception date. LMP is the most common method used by healthcare providers. If you know your exact conception date (from fertility tracking or IVF), that method provides a slightly more precise estimate.
- Enter the relevant date using the date picker. For LMP, enter the first day of your last menstrual period. Pregnancy is dated from this day, even though conception typically occurs about 2 weeks later. This means you are already considered 2 weeks pregnant on the day you actually conceive.
- View your estimated due date (EDD), current gestational week, and trimester. The standard calculation adds 280 days (40 weeks) to your LMP date, known as Naegele's rule. Your due date is the midpoint of a normal delivery window — only about 4% of babies are born on their exact due date.
- Review key pregnancy milestones mapped to your personal timeline: when the heartbeat is detectable (week 6-7), when genetic screening is available (weeks 10-13), the anatomy scan (week 18-20), viability threshold (week 24), and full term (week 39-40).
- Track your prenatal appointment schedule based on standard guidelines. Visits are typically monthly until week 28, biweekly from weeks 28-36, and weekly from week 36 until delivery. Each visit includes specific tests and screenings appropriate to that gestational stage.
- Share your due date and weekly progress with your partner, family, or healthcare team. Keep in mind that the due date may be adjusted after your first ultrasound if the measured gestational age differs from the LMP calculation by more than 5-7 days.
Frequently asked questions
How is a pregnancy due date calculated?
The standard method (Naegele's rule) adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day menstrual cycle with ovulation occurring on day 14. If your cycle is longer or shorter than 28 days, your due date may shift. For a 35-day cycle, ovulation likely occurs around day 21, so add 7 days to the Naegele estimate. Ultrasound dating in the first trimester (weeks 7-12) is the most accurate method, measuring the crown-rump length of the embryo. If ultrasound dating differs from LMP by more than 5-7 days, your healthcare provider will adjust the due date.
How accurate is a due date calculator?
Due date calculations provide an estimate, not a guaranteed delivery date. Only about 4% of babies are born on their exact due date. However, approximately 80% are born within 2 weeks of the estimated date (between weeks 38 and 42). First-time mothers tend to deliver slightly later than their due date on average. Ultrasound dating in the first trimester is accurate to within 3-5 days. LMP-based calculations are accurate to within 7-10 days when cycle length is known. The due date becomes more of a target range than a specific date — full term is defined as 39 weeks 0 days through 40 weeks 6 days.
What are the three trimesters?
First trimester (weeks 1-12): rapid cell division, organ formation, and development of the neural tube, heart, and brain. Morning sickness peaks around weeks 8-10. Risk of miscarriage decreases significantly after week 12. Second trimester (weeks 13-27): often called the easiest trimester. The baby grows rapidly, movements become noticeable around weeks 18-22, and the anatomy scan at weeks 18-20 checks for structural development. Third trimester (weeks 28-40): the baby gains weight rapidly (about 0.5 lb per week), lungs mature, and the baby positions for delivery, usually head-down by weeks 32-36.
When should I see a doctor after a positive test?
Schedule your first prenatal appointment for 6-8 weeks after your last menstrual period. This timing allows the pregnancy to be confirmed on ultrasound (heartbeat visible at 6-7 weeks). If you have a history of complications, ectopic pregnancy, or severe symptoms (heavy bleeding, severe pain), contact your healthcare provider immediately. At your first visit, expect a full medical history, blood tests (blood type, Rh factor, CBC, STI screening, immunity checks), urine tests, blood pressure measurement, and an early ultrasound. In Canada, prenatal care is fully covered by provincial health insurance.
Can my due date change?
Yes, due dates are commonly adjusted after the first ultrasound (7-12 weeks). If the ultrasound measurement of the embryo suggests a gestational age that differs by more than 5-7 days from your LMP calculation, the due date will be revised to match the ultrasound. Later ultrasounds are less accurate for dating because fetal growth rates vary more in the second and third trimesters. Your due date may also shift if your initial LMP date was incorrect, if you have irregular cycles, or if the pregnancy was conceived through IVF (in which case the transfer date provides exact dating).
What is considered full term pregnancy?
The American College of Obstetricians and Gynecologists defines: early term (37-38 weeks 6 days), full term (39 weeks to 40 weeks 6 days), late term (41 weeks to 41 weeks 6 days), and post-term (42 weeks and beyond). Babies born at 39-40 weeks have the best outcomes, which is why elective inductions and C-sections are generally not recommended before 39 weeks without medical indication. After 41 weeks, healthcare providers typically begin monitoring more closely and may recommend induction between 41 and 42 weeks due to increased risk of complications.
How does pregnancy dating work for IVF?
For IVF pregnancies, dating is more precise because the exact dates of egg retrieval and embryo transfer are known. For a day-3 embryo transfer, add 263 days (or subtract 3 days from transfer date and count 40 weeks). For a day-5 blastocyst transfer, add 261 days (or subtract 5 days from transfer date and count 40 weeks). The resulting due date is typically more accurate than LMP-based calculations because it eliminates uncertainty about ovulation timing. Most IVF clinics still confirm dating with a first-trimester ultrasound.
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