Pregnancy Due Date Calculator

The standard method is Naegele's rule, developed in the 19th century and still used universally: Due Date = First day of Last Menstrual Period (LMP) + 280 days (40 weeks). The formula assumes a 28-day menstrual cycle with ovulation on day 14. If your cycle differs, the due date adjusts accordingly - a 32-day cycle (ovulation day 18) shifts the due date 4 days later; a 24-day cycle (ovulation day 10) shifts it 4 days earlier. This is why an accurate LMP date and cycle length are both important inputs. Most importantly, if an early ultrasound (ideally done at 6-12 weeks) shows fetal size that differs from LMP-based gestational age by more than 7-10 days, Indian obstetric guidelines recommend adjusting the EDD to match ultrasound measurements - sonography is more accurate than LMP recall, particularly for women with irregular cycles. Only about 4% of babies are actually born on their estimated due date; 80% are born within 2 weeks either side.

Pregnancy is divided into three trimesters, each with distinct developmental milestones. First trimester (Weeks 1-12): Encompasses the embryonic period (weeks 3-8) when all major organs and structures form. Morning sickness, fatigue, and breast tenderness are common. The nuchal translucency ultrasound at 11-13 weeks screens for chromosomal anomalies. Second trimester (Weeks 13-27): Often called the golden trimester as morning sickness typically resolves by week 14. Fetal movements (quickening) are felt by most mothers at 18-22 weeks. The mid-trimester anatomy scan (TIFFA) at 18-22 weeks is the most detailed ultrasound of the pregnancy. Third trimester (Weeks 28-40): Rapid fetal weight gain - from approximately 1 kg at 28 weeks to 3-3.5 kg at term. Birth timing: before 37 weeks is preterm, 37-38 weeks is early term, 39-40 weeks is full term. Indian obstetric guidelines recommend against elective delivery before 39 weeks due to higher respiratory complications in early-term babies.

IVF due date calculation accounts for the embryo's known age at the time of transfer. For a 5-day blastocyst transfer (the most common type in modern IVF clinics in India): the LMP equivalent = Transfer Date minus 17 days, giving a due date of Transfer Date + 261 days. For a 3-day embryo transfer: the LMP equivalent = Transfer Date minus 17 days, but 2 additional days are subtracted because the embryo is younger. For frozen embryo transfer (FET): the calculation uses the same LMP equivalent method as fresh 5-day transfer. The gestational age on the day of transfer itself is typically 5 weeks and 2 days as counted from LMP equivalent. IVF pregnancies are measured from the LMP equivalent, not from egg retrieval or fertilization date, so that gestational week numbers remain consistent with natural conceptions. All IVF due dates should be confirmed by the treating fertility clinic and validated with the first ultrasound at 6-7 weeks post-transfer.

The anatomy scan, called the TIFFA scan (Targeted Imaging for Fetal Anomalies) in India, is a detailed ultrasound performed between weeks 18-22 of pregnancy (ideally at 20-21 weeks when anatomical structures are clearest). It systematically evaluates: brain and spine structure, heart anatomy (four chambers, outflow tracts), abdominal wall, kidneys and bladder, limb bones, placenta position, amniotic fluid volume, and umbilical cord vessels. This is also when fetal sex can typically be identified, though sex determination disclosure is legally prohibited in India under the PCPNDT Act 1994. The TIFFA scan does not detect all anomalies - conditions affecting chromosomes, metabolism, or brain development that appear later in pregnancy will not be visible at 20 weeks. A normal TIFFA scan significantly reduces but does not eliminate the risk of structural birth defects. It should be performed by a trained maternal-fetal medicine sonographer.

Gestational age in obstetrics is expressed in completed weeks plus remaining days - written as W+D. For example, 8+3 means 8 complete weeks and 3 additional days have passed since the LMP date (a total of 59 days). The week number always represents completed weeks, not the current week - so 8+3 means you are in your 9th week of pregnancy. Key milestones in this notation: 0+0 is your LMP date; 4+0 is when a missed period typically occurs; 6+0 to 7+0 is when a fetal heartbeat is first detectable by transvaginal ultrasound; 12+0 is the end of the first trimester; 20+0 is the midpoint and typical anatomy scan week; 37+0 is early term; 40+0 is the estimated due date. Many pregnant women in India track their pregnancy using apps that describe the baby's size compared to a fruit - these apps use completed weeks, so when they say week 8, they mean 8 complete weeks (56 days from LMP), consistent with the obstetric convention.

LMP (Last Menstrual Period) date is the first day of your last normal menstrual period before conception - it is the anchor point for all gestational age calculations. EDD (Estimated Delivery Date) and EDC (Estimated Date of Confinement) mean exactly the same thing - the predicted due date, typically 40 weeks from LMP. EDC is older clinical terminology; EDD is the preferred modern term used by obstetricians. In India, some doctors still use EDC on prescriptions. Both are calculated identically: LMP date + 280 days = EDD = EDC. Gestational age is always calculated from LMP, not from conception date - this is why a pregnancy is described as 40 weeks long even though fertilisation occurs at approximately week 2 and implantation at approximately week 3. The 2-week discrepancy between LMP and conception date is embedded in all obstetric conventions and should not be adjusted away.

The due date is an estimate, not a deadline. Only approximately 4 to 5% of babies are born on their exact EDD. Most births (approximately 80%) occur within 2 weeks before or after the EDD. About 10% of pregnancies last beyond 42 weeks (post-term). First-time mothers tend to deliver slightly later than the EDD on average; mothers who have delivered before tend to deliver earlier. The EDD is most accurate when established by an early ultrasound at 6 to 12 weeks (margin of error plus or minus 5 to 7 days) compared to LMP-based calculation (margin of error plus or minus 14 to 21 days for women with irregular cycles). Indian obstetric practice considers 37 to 41 completed weeks as normal term. Medical induction is typically considered at or after 41 weeks if labour has not begun naturally. Regular antenatal check-ups every 4 weeks through week 28, then every 2 weeks through week 36, then weekly from week 37 are the standard monitoring schedule in Indian hospitals.