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Calculate your due date, track your pregnancy progress, and discover important milestones throughout your journey.
Most common method - uses Naegele's rule (LMP + 280 days)
Results will appear here after calculation
Evidence-based obstetric science since 1756
280
Days average pregnancy
3
Trimesters
40
Weeks gestational
1756
Year Naegele's Rule established
A due date, formally called the Estimated Date of Delivery (EDD) or Estimated Date of Confinement (EDC), marks the end of an average full-term pregnancy of 40 weeks (280 days) counted from the first day of the last menstrual period (LMP). The 40-week framework exists because most women ovulate around day 14 of their cycle, so the true fertilization window is approximately 2 weeks after the LMP begins.
In clinical practice, gestational age is measured from LMP even though the embryo is actually about 2 weeks younger than the gestational age suggests. This convention was standardized long before reliable conception-date testing was possible and remains universal today.
The most widely used method for calculating due dates is Naegele's Rule, formulated by German obstetrician Franz Karl Naegele in 1756. The formula is elegantly simple:
Due Date = LMP + 280 days
Equivalently: LMP + 9 calendar months + 7 days
Example: LMP = January 1 → Due Date = October 8
Clinical Note: First-trimester ultrasound (before 14 weeks) is considered the gold standard for dating accuracy, achieving a margin of error of ±3–5 days. After the first trimester, accuracy decreases and an LMP-based date is generally not revised.
| Week | Trimester | Key Milestone | Baby Size Reference |
|---|---|---|---|
| W4 | 1st | Embryo implants in uterine wall; neural tube begins forming | Poppy seed (~2 mm) |
| W8 | 1st | Heart beating; limb buds present; all major organs forming | Raspberry (~1.6 cm) |
| W12 | 1st | Nuchal translucency scan; all organs formed; miscarriage risk drops sharply | Lime (~5.4 cm) |
| W16 | 2nd | Gender often visible on ultrasound; baby makes facial expressions | Avocado (~11.6 cm) |
| W20 | 2nd | Anatomy scan; halfway point; many mothers first feel kicks | Banana (~25 cm) |
| W24 | 2nd | Viability threshold; lungs developing; baby responds to sound | Corn cob (~30 cm) |
| W28 | 3rd | Eyes open; REM sleep cycles; glucose tolerance screening | Eggplant (~37 cm) |
| W32 | 3rd | Rapid weight gain; lungs nearly mature; baby may turn head-down | Butternut squash (~42 cm) |
| W36 | 3rd | Baby drops into pelvis (lightening); cervix may begin softening | Honeydew melon (~47 cm) |
| W40 | 3rd | Estimated due date; fully developed; average weight ~3.4 kg / 7.5 lb | Small pumpkin (~51 cm) |
| Week Range | Visit Frequency | Tests & Screenings |
|---|---|---|
| Wk 4–8 | Initial booking visit | Blood type, Rh factor, CBC, rubella immunity, STI screening, urine culture, genetic counseling referral |
| Wk 8–13 | Once | Nuchal translucency ultrasound; cell-free DNA / NIPT (optional); chorionic villus sampling if indicated |
| Wk 14–27 | Every 4 weeks | Anatomy scan at 18–22 weeks; AFP/quad screen at 15–20 weeks; amniocentesis if indicated |
| Wk 28–35 | Every 2 weeks | Glucose challenge test at 24–28 weeks; Tdap vaccine at 27–36 weeks; RhoGAM for Rh-negative patients |
| Wk 36–40 | Weekly | Group B Strep (GBS) culture at 35–37 weeks; fetal position check; cervical exam; biophysical profile if post-term |
Based on the 2009 Institute of Medicine (IOM) guidelines, adopted by ACOG.
| Pre-pregnancy BMI | Category | Total Recommended Gain | Weekly Gain (2nd–3rd Trimester) |
|---|---|---|---|
| < 18.5 | Underweight | 12.5–18 kg (28–40 lb) | ~0.5 kg / ~1 lb |
| 18.5–24.9 | Normal weight | 11.5–16 kg (25–35 lb) | ~0.4 kg / ~1 lb |
| 25.0–29.9 | Overweight | 7–11.5 kg (15–25 lb) | ~0.3 kg / ~0.6 lb |
| ≥ 30.0 | Obese | 5–9 kg (11–20 lb) | ~0.2 kg / ~0.5 lb |
| Any (twins) | Twin pregnancy | 17–25 kg (37–54 lb) | ~0.7 kg / ~1.5 lb |
* Consult your healthcare provider for personalized recommendations.
1756
Naegele's Rule formulated
Franz Karl Naegele publishes his due-date calculation method (LMP + 280 days), establishing the framework still used worldwide today.
1827
Egg cell discovered
Karl Ernst von Baer identifies the human ovum, revolutionizing understanding of fertilization and conception timing in mammals.
1950s
Obstetric ultrasound begins
Ian Donald pioneers obstetric ultrasound in Glasgow, offering real-time fetal imaging and a new, more accurate route to dating gestational age.
1978
First IVF birth
Louise Brown is born via in vitro fertilization, bringing precise date-of-conception knowledge and new due-date calculation methods for assisted reproduction.
1990s
Prenatal genetic testing advances
First-trimester combined screening and amniocentesis become routine, enabling chromosomal analysis alongside gestational age confirmation.
2000s
3D/4D ultrasound era
Three-dimensional and real-time 4D ultrasound imaging bring detailed anatomical views, improving fetal growth assessment and anomaly detection.
Assumes a perfectly regular 28-day cycle with ovulation on day 14. Studies show accuracy within ±2 weeks in most regular-cycle pregnancies.
Margin: ±10–14 days
Crown-rump length measurement before 14 weeks is the most precise dating tool available in clinical practice.
Margin: ±3–5 days
Later scans assess head circumference, femur length, and abdominal circumference. Normal biological variation increases the error window.
Margin: ±2–3 weeks
Only about 4–5% of babies are born exactly on their estimated due date. Natural labor is triggered by a complex cascade of hormonal signals from both baby and mother, with biological variability spanning several weeks. A term birth is defined as 37–42 weeks gestation. Babies born between 37 and 41 weeks and 6 days are considered "term" without medical concern about gestational age alone.
ACOG Practice Bulletin
ACOG recommends ultrasound in the first trimester as the gold standard for gestational age assignment when discordant by more than 5 days from LMP-based estimates.
ACOG Committee Opinion No. 700 →British Medical Journal
Multinational BMJ research shows spontaneous births cluster between 38 and 42 weeks, with the median at 39.5 weeks, reinforcing that 40-week due dates are estimates, not targets.
Morken et al., BMJ Open, 2014
WHO Guidelines
The World Health Organization recommends a minimum of 8 antenatal care contacts for a positive pregnancy experience, with early booking before 12 weeks whenever possible.
WHO ANC Model 2016 →Myth
Your due date is an exact prediction of when your baby will be born.
Fact
Only 4–5% of babies are born on their due date. Most arrive within 2 weeks before or after. The due date is the midpoint of a normal distribution of labor onset, not a deadline.
Myth
Morning sickness only happens in the morning.
Fact
Despite the name, nausea and vomiting can happen at any time of day or night. About 80% of pregnant women experience nausea, and for many it is persistent throughout the day, especially in the first trimester.
Myth
You need to "eat for two" during pregnancy.
Fact
You only need an extra ~300 calories per day in the second and third trimesters — roughly equivalent to a healthy snack, not a full additional meal. Excessive caloric intake increases gestational weight gain risks.
Myth
Heartburn during pregnancy means your baby will have lots of hair.
Fact
While one small Johns Hopkins study found a weak correlation, heartburn is overwhelmingly caused by progesterone relaxing the lower esophageal sphincter and the growing uterus putting upward pressure on the stomach.
Myth
Exercise is dangerous during pregnancy.
Fact
For low-risk pregnancies, ACOG actively recommends 150 minutes of moderate-intensity aerobic activity per week. Exercise reduces risk of gestational diabetes, preeclampsia, excessive weight gain, and cesarean delivery.
Myth
If the fetal heartbeat is fast, it's a girl; slow means a boy.
Fact
No scientific evidence supports fetal heart rate as a reliable sex predictor. The average fetal heart rate is 120–160 bpm in both sexes, varying with gestational age and activity level rather than sex.
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