Pregnancy Due Date Calculator — When Is My Baby Due?
Calculate your estimated due date (EDD) from your last menstrual period (LMP) or conception date using Naegele's Rule. Get gestational age, current trimester, days remaining, key prenatal appointment schedule, and baby size by week.
Group B Streptococcus vaginal/rectal swab — determines antibiotic need in labor
36–40 Weeks
Weekly Appointments
Cervical exam, fetal position, NST if post-term, birth plan finalization
Pregnancy Trimesters — What to Expect
Trimester
Weeks
Description
Key Events
First Trimester
Weeks 1–13
Major organ formation. Highest miscarriage risk (~80% of losses occur here). Common symptoms: morning sickness (weeks 6–9), fatigue, breast tenderness, frequent urination.
Often called the 'golden trimester' — energy returns, nausea improves, baby bump visible. Baby begins moving (quickening, weeks 16–22). Most comfortable trimester for most women.
Pregnancy Due Date Calculator — How Your EDD Is Calculated
The Estimated Due Date (EDD) is calculated using Naegele's Rule, developed by German obstetrician Franz Karl Naegele in 1812.
The formula: EDD = First day of LMP + 280 days (40 weeks).
This assumes a 28-day menstrual cycle with ovulation occurring on Day 14. If your cycle differs, this calculator adds or subtracts days proportionally.
The 280-day figure represents the average gestation from LMP — 266 days from actual conception (since conception typically occurs at Day 14 of the cycle).
Why the Due Date Is an Estimate — Not a Deadline
Only about 4–5% of babies are born on their exact due date.
A normal full-term delivery occurs anywhere from 37 to 42 weeks of gestation.
The American College of Obstetricians and Gynecologists (ACOG) categorizes term pregnancy as: Early term (37–38⁶⁄₇ weeks), Full term (39–40⁶⁄₇ weeks), Late term (41–41⁶⁄₇ weeks), and Post-term (42+ weeks).
First-trimester ultrasound dating (7–13 weeks) is the most accurate method and typically supersedes LMP dating when there is a discrepancy of more than 5–7 days.
IVF Due Date Calculation
For IVF pregnancies, due date calculation differs based on embryo age at transfer:
Day 3 embryo transfer: EDD = Transfer date + 263 days (adds 17 days before LMP would have occurred).
Day 5 blastocyst transfer: EDD = Transfer date + 261 days.
IVF due dates are highly accurate because the exact fertilization date is known, eliminating the uncertainty of natural conception dating.
If you are unsure of your LMP date, the most reliable option is a first-trimester ultrasound (7–13 weeks). The ultrasound technician measures crown-rump length (CRL) to determine gestational age with a margin of error of only ±5–7 days — significantly more accurate than LMP-based calculation in women with irregular cycles. After 13–14 weeks, ultrasound accuracy decreases to ±2 weeks due to normal variation in fetal growth. Your OB or midwife may adjust your EDD based on ultrasound findings at the first prenatal visit — this is called "redating" and is common when LMP-based and ultrasound-based dates differ by more than 7–10 days.
Can I go into labor before or after my due date?
Yes — the due date is a statistical midpoint, not a deadline. Labor can begin naturally anytime from 37–42 weeks (full to post-term). About 11% of births occur before 37 weeks (preterm); 26% occur after 40 weeks. If labor doesn't start by 41–42 weeks, your care provider will typically recommend monitoring and may discuss induction to reduce risks associated with post-term pregnancy (placental aging, meconium aspiration risk, stillbirth risk increases after 42 weeks). Signs of labor: regular contractions that increase in frequency and intensity, water breaking (rupture of membranes), bloody show (mucus plug discharge). Braxton Hicks contractions (practice contractions, irregular and not painful) are normal from the second trimester onward and do not indicate true labor.
What is the difference between gestational age and fetal age?
Gestational age is measured from the first day of the last menstrual period (LMP) — this is the standard used by all OBs, midwives, and this calculator. Fetal age (embryonic age or fertilization age) is measured from the date of conception/fertilization — typically 2 weeks LESS than gestational age. So when your OB says you are "8 weeks pregnant," the embryo is actually only about 6 weeks old from fertilization. Ultrasound reports and all prenatal milestones use gestational age from LMP. If you enter a conception date in this calculator, we add 14 days to convert it to gestational age for the EDD calculation.
When should I call my doctor or go to the hospital?
Call your OB or go to the hospital immediately for any of these: Heavy vaginal bleeding (more than a period); Severe abdominal pain or cramping; Signs of preeclampsia — severe headache, visual disturbances (flashing lights), sudden severe swelling of face/hands, upper right abdominal pain; Decreased or absent fetal movement after 28 weeks (less than 10 movements in 2 hours); Signs of preterm labor before 37 weeks — regular contractions every 10 minutes or closer, lower back pain, pelvic pressure, or fluid leakage; Water breaking (rupture of membranes) — even without contractions; High fever (>100.4°F / 38°C); Signs of deep vein thrombosis — calf pain, swelling, warmth (pregnancy increases clot risk significantly).