Advanced Pregnancy Due Date Calculator

Due dates are calculated using Naegele's Rule: LMP + 280 days (40 weeks). This assumes a 28-day cycle and ovulation on day 14. For irregular cycles, our calculator adjusts: LMP + 280 + (cycle length - 28). For conception dates, it's conception + 266 days (38 weeks). For IVF, transfer date is adjusted based on embryo age (Day 3 or Day 5).

Only about 4-5% of babies are born on their exact due date. About 80% are born within 2 weeks before or after. First-time mothers often deliver slightly past their due date. Ultrasound dating in the first trimester (7-12 weeks) is most accurate, with margin of error of ±7 days.

LMP (Last Menstrual Period) is the first day of your last period—this is how doctors count pregnancy weeks, even though conception hasn't occurred yet. Conception typically happens ~14 days after LMP during ovulation. If you know your ovulation/conception date (from tracking or IVF), you can use that directly for a more precise calculation.

For irregular cycles: 1) Use our adjustable cycle length feature if you know your average cycle, 2) Use conception date if you tracked ovulation, 3) Get an early dating ultrasound (most accurate). With very irregular cycles, LMP-based calculations may be off by weeks—ultrasound is recommended.

Naegele's Rule, developed by German obstetrician Franz Naegele in the 1800s, calculates EDD as: LMP + 1 year - 3 months + 7 days. This equals LMP + 280 days. It assumes a 28-day cycle with ovulation on day 14. Despite being 200+ years old, it remains the standard method used worldwide.

First Trimester (Weeks 1-12): Major organ development, highest miscarriage risk, morning sickness common. Second Trimester (Weeks 13-26): Energy returns, baby movement felt, anatomy scan around week 20. Third Trimester (Weeks 27-40): Rapid growth, preparing for birth, nesting instinct, more frequent prenatal visits.

Baby's heartbeat can be detected by transvaginal ultrasound around 6 weeks (when heart starts beating at 100-120 bpm). By 8 weeks, it's clearly visible. With a Doppler device at home or doctor's office, you may hear it around 10-12 weeks. Heart rate peaks at 9-10 weeks (170 bpm) then settles to 120-160 bpm.

24 weeks is considered the 'age of viability'—when babies have a realistic chance of survival if born early with intensive medical care. Survival rates: ~50% at 24 weeks, ~80% at 26 weeks, ~90% at 28 weeks. Before 24 weeks, survival is possible but rare and often with significant complications.

The anatomy scan (Level 2 ultrasound) at 18-22 weeks examines: baby's organs (heart, brain, kidneys, liver), spine, limbs, facial features, placenta position, amniotic fluid levels, umbilical cord, and often reveals gender if desired. It can detect many structural abnormalities. Takes 30-60 minutes.

Term definitions: Early Term (37w0d - 38w6d), Full Term (39w0d - 40w6d), Late Term (41w0d - 41w6d), Post Term (42w+). Babies born at 39+ weeks have better outcomes than 37-38 weeks. This is why scheduled deliveries should wait until 39 weeks unless medically indicated.

For IVF pregnancies: Day 5 embryo transfer: Due date = Transfer date + 261 days (38 weeks minus 5 days). Day 3 embryo transfer: Due date = Transfer date + 263 days. This accounts for embryo age. IVF dating is typically very accurate because conception timing is precisely known.

Yes. Doctors may adjust your due date if early ultrasound measurements differ significantly from LMP dating (usually >5-7 days difference). Once dating is established by first-trimester ultrasound, it typically doesn't change. Later ultrasounds are less accurate for dating due to natural size variations.

Going past EDD is common—about 50% of pregnancies do. Monitoring increases (often twice weekly) after 40 weeks. Most doctors discuss induction between 41-42 weeks due to slightly increased risks after 42 weeks. Factors considered: placenta function, amniotic fluid, baby's movement, maternal health.

Many wait until after 12 weeks when miscarriage risk drops significantly (~80% of miscarriages occur in first trimester). However, some announce earlier to close family for support. After a healthy anatomy scan (20 weeks) is another common 'all clear' point. There's no medical rule—it's personal preference.

Important dates: Week 8 (first prenatal visit), Week 10-13 (NIPT/first-trimester screening), Week 12 (end of first trimester), Week 16 (start feeling movement), Week 20 (anatomy scan), Week 24 (viability), Week 28 (glucose test), Week 36 (weekly visits begin), Week 37 (early term), Week 39 (full term), Week 40 (EDD).