Pregnancy Calculator

How is Pregnancy Calculated?

Pregnancy duration is counted from the first day of your Last Menstrual Period (LMP), not from conception. A full-term pregnancy is 40 weeks (280 days) from LMP. This follows ACOG's due date convention (LMP + 280 days, assuming a 28-day cycle with ovulation on day 14; ACOG). The cycle-length option is a conventional rough calendar adjustment, not a guideline recommendation: it assumes ovulation about 14 days before your next period, so the due date and the week count shift by (cycle length minus 28) days. It cannot be precise, especially with irregular cycles. Ultrasound dating can replace LMP dating.

What are the Trimesters?

ACOG groups the 40 weeks into three trimesters: First (from the first day of LMP to 13 weeks 6 days), Second (14 weeks 0 days to 27 weeks 6 days) and Third (28 weeks 0 days onward). ACOG's term labels are early term 37w 0d to 38w 6d, full term 39w 0d to 40w 6d, late term 41w 0d to 41w 6d and postterm from 42w 0d. Sources: ACOG, ACOG Committee Opinion 579.

When to See a Doctor?

Key antenatal checkup windows: 8–12 weeks, 16–20 weeks (anomaly scan), 24–28 weeks (glucose test), 32–36 weeks, and 38–40 weeks. Always consult a qualified gynaecologist for medical advice.