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Pregnancy Due Date Calculator

Enter your last menstrual period (LMP) to estimate due date, current weeks pregnant, trimester and major milestones. Uses Naegele's rule (LMP + 280 days).

🔒 Runs entirely in your browser — no data sent to any server.

How the due date is estimated

Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period. It assumes a 28-day cycle with ovulation on day 14. Most Indian obstetricians confirm the LMP-based estimate with a first-trimester ultrasound (typically the dating scan at 7–9 weeks) and adjust by a few days if needed.

If your cycle isn't 28 days

A 32-day cycle pushes ovulation to roughly day 18, so the calculated due date based on LMP alone runs about 4 days early. A 26-day cycle runs 2 days late. Doctors generally accept the LMP-based date unless an ultrasound disagrees by more than 7 days in the first trimester or 14 days later on — at which point the scan date wins.

Trimester milestones in India

  • Weeks 1–13 (first trimester): NT scan around 11–13 weeks, dual marker test (PAPP-A, free β-hCG).
  • Weeks 14–27 (second trimester): anomaly / TIFFA scan around 20 weeks, glucose challenge test for gestational diabetes around 24–28 weeks.
  • Weeks 28–40 (third trimester): growth scans every 4 weeks, Tdap booster around 27–36 weeks, GBS swab close to delivery.

Related

For child immunisation timing after birth, see the vaccination tracker (covers IAP and national schedules). For child growth-curve percentiles, see the IAP child growth tool. Pregnancy is also when many couples re-look at term insurance and emergency-fund needs — see the emergency fund calculator.

For educational use only

This calculator is a planning aid, not a medical diagnosis. Always confirm your due date and pregnancy progress with an obstetrician. Runs entirely in your browser — no data is sent to any server.

FAQ

How accurate is the LMP method?

For regular 28-day cycles: ±5-7 days. For irregular cycles or PCOS: confirm with first-trimester ultrasound. Actual delivery: ±2 weeks of due date is normal.

IVF — does the calculator work?

For IVF, the "LMP" is the embryo transfer date minus 14 days (for Day-5 embryo) or 17 days (for Day-3). Most fertility centres provide adjusted due dates.

Can I deliver before 37 weeks?

Pre-term: < 37 weeks. Risks of prematurity rise as weeks decrease. Most modern hospitals can support delivery from 24+ weeks; outcomes improve dramatically after 32 weeks.