Pregnancy Due Date Calculator

This pregnancy due date calculator estimates your estimated due date (EDD), your current gestational age week by week, and the major clinical milestones of pregnancy. It supports the three methods used in obstetric practice: Naegele's rule from the last menstrual period (LMP), conception-date dating, and ultrasound (sonographic) dating — so you can use whichever information your doctor has given you.

It is built for expectant mothers, partners, and families who want a clear, private snapshot of how far along the pregnancy is and what is coming next. Pick a method, enter the relevant date, and the calculator works out your EDD, how many weeks and days pregnant you are today, your current trimester, and a timeline of scans and checkpoints. It is an informational planning aid, not a substitute for antenatal care.

How the due date is calculated (Naegele's rule)

EDD = LMP + 280 days + (cycleLength − 28)

Pregnancy is counted from the first day of your last menstrual period, even though conception usually occurs around two weeks later — which is why you are already counted as about 2 weeks pregnant at conception. The cycle-length adjustment nudges the EDD earlier or later to account for ovulation that happens before or after the textbook 28-day midpoint. The conception method instead adds 266 days to a known conception date, and the ultrasound method back-calculates an effective LMP from the gestational age measured at the scan, then adds 280 days.

A worked example

Say the first day of your last period was 1 January 2026 with a regular 28-day cycle. Adding 280 days gives an EDD near 8 October 2026. If today is around 17 May 2026, you would be roughly 19 weeks pregnant — in the second trimester, just before the anatomy scan. Change the "Compute as of" date to see your gestational age at any past or future point, which is handy for planning leave or travel.

Ultrasound dating

A first-trimester ultrasound (between weeks 8 and 13) measures the embryo's crown-rump length and produces a gestational age that is typically accurate to within about ±5 days. Per ISUOG guidance, if ultrasound dating differs from LMP-based dating by more than seven days, the ultrasound date is used as the official EDD. This is why your gynaecologist may re-date your pregnancy after the first scan — the scan is generally the more reliable anchor.

Gestational age vs fetal age

Two clocks are often confused. Gestational age is counted from the first day of your LMP and is the figure your doctor and every scan report use. Fetal (embryonic) age is counted from conception and is about two weeks less. So "12 weeks pregnant" (gestational) corresponds to a fetus roughly 10 weeks old. This calculator reports gestational age, matching clinical practice in India.

Trimesters and milestones

First trimester covers weeks 1–12, second trimester weeks 13–27, and third trimester weeks 28–40. Key clinical milestones include the first-heartbeat scan around week 6, the NT (nuchal translucency) scan at weeks 11–13, the anatomy / Level-2 scan at weeks 18–22, the viability milestone at week 24, full term from week 37, the estimated due date at week 40, and the post-term threshold at week 42. Indian antenatal care also schedules iron-folic-acid supplementation, the Tdap vaccine, and gestational-diabetes screening (24–28 weeks) around these weeks.

Key tips and common notes

• Only about 5% of babies arrive on their EDD. Most are born between weeks 37 and 42, so treat the due date as the centre of a window.
• Match the method to your data. Use ultrasound if your doctor dated the pregnancy by scan; use LMP only if you are confident of the date and your cycles are regular.
• Adjust your cycle length. If your cycle is not 28 days, set it so the EDD reflects your real ovulation timing.
• Re-check after the first scan. If the scan moves your dates, update the inputs here to keep the milestone timeline accurate.

This calculator is for general information and planning only — it is a screening aid, not medical advice. Your due date, gestational age, and pregnancy care should always be confirmed and managed by your doctor or gynaecologist.