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Pregnancy Due Date Calculator
Calculate your due date and pregnancy milestones
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What is the Pregnancy Due Date Calculator?
The Pregnancy Due Date Calculator estimates your baby's expected arrival date and maps out your entire pregnancy week by week. You can calculate from the first day of your last menstrual period (LMP), your estimated conception date, or your IVF embryo transfer date. The calculator uses Naegele's rule — the gold-standard obstetric formula — and shows your current pregnancy week, progress bar, trimester boundaries, and key prenatal milestones with their expected calendar dates.
How to Use the Due Date Calculator
- 1.Select your calculation method: Last Period (LMP), Conception Date, or IVF Transfer Date.
- 2.Enter the relevant date. For LMP, use the first day of your last period. For conception, enter when conception occurred. For IVF, enter your embryo transfer date and select Day 3 or Day 5 embryo.
- 3.Your estimated due date appears instantly, along with your current pregnancy week and progress percentage.
- 4.Review the trimester boundaries and key milestone dates — helpful for planning prenatal appointments and scans.
Frequently Asked Questions
How is the due date calculated from LMP?+
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 with ovulation on day 14. The formula dates to 1812 and remains the obstetric standard today. If you have irregular cycles, your doctor may use a first-trimester ultrasound measurement of the crown-rump length (CRL) to adjust the due date, which can be accurate to within 5–7 days.
How accurate is the due date calculation?+
The calculated due date is an estimate — only around 4–5% of babies are born on their exact due date. About 80% of births occur within two weeks before or after the due date. The most accurate due dates come from first-trimester ultrasound measurements of the embryo's crown-rump length (CRL), which can pin the date to within 5 days. Due dates from LMP can be off by up to 2–3 weeks for women with irregular cycles.
What is the difference between gestational age and fetal age?+
Gestational age counts from the first day of your last menstrual period — this is the age your doctor references on all prenatal charts and forms. Fetal age (or embryonic age) counts from the actual day of conception, which is typically 2 weeks after LMP. A pregnancy that is 10 weeks gestational age is approximately 8 weeks from conception. Healthcare providers almost always use gestational age because LMP is easier to know precisely than the exact day of conception.
How does the IVF transfer date calculation work?+
For IVF pregnancies, the due date depends on the age of the embryo at transfer. A Day 5 blastocyst transfer: the due date is transfer date + 261 days (because the embryo is equivalent to day 19 of a standard 280-day pregnancy). A Day 3 embryo transfer: due date = transfer date + 263 days (equivalent to day 17). This calculator handles both scenarios — simply select the correct embryo day before entering your transfer date.
What are the three trimesters of pregnancy?+
Pregnancy is divided into three trimesters. The first trimester covers weeks 1–12 (from LMP). Key events include implantation, formation of all major organs, and the highest risk of miscarriage (which drops significantly after week 10). The second trimester covers weeks 13–27 — the 'golden period' when nausea often eases, energy returns, and the anatomy scan (weeks 18–20) reveals the baby's sex and screens for structural abnormalities. The third trimester covers weeks 28–40, during which the baby gains most of its weight and prepares for birth.
What is considered full term in pregnancy?+
A full-term pregnancy is 39 to 40 weeks and 6 days of gestational age. The American College of Obstetricians and Gynecologists (ACOG) defines: Early term: 37 weeks 0 days to 38 weeks 6 days; Full term: 39 weeks 0 days to 40 weeks 6 days; Late term: 41 weeks 0 days to 41 weeks 6 days; Post term: 42 weeks 0 days and beyond. Babies born at 37 weeks are considered 'early term' rather than premature, but outcomes are generally good. Elective inductions before 39 weeks are typically avoided unless medically necessary.
What are the most important prenatal appointments and tests?+
Key milestones include: Week 8 — first prenatal visit with full blood panel; Weeks 10–13 — first trimester screening (NIPT blood test for chromosomal conditions, nuchal translucency ultrasound); Weeks 16–18 — quad screen blood test option; Weeks 18–20 — anatomy scan ultrasound; Weeks 24–28 — glucose tolerance test for gestational diabetes; Week 28 — Rh antibody check and Tdap vaccine; Weeks 35–37 — Group B Strep (GBS) culture; Weeks 36–40 — weekly appointments to check cervical dilation and baby's position.