Pregnancy Due Date Calculator
Estimate your baby's due date based on your last menstrual period (LMP).
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Pregnancy Due Date Calculator
Generated on April 24, 2026
?What is the Pregnancy Due Date Calculator?
This pregnancy calculator uses Naegele's rule (LMP + 280 days) — the standard obstetric method worldwide — adjusted for your individual cycle length if different from the default 28 days. It gives your estimated due date, probable conception date, trimester boundaries, and current pregnancy progress in weeks and days. This is useful for expecting mothers planning their prenatal schedule, partners and family tracking milestones, and healthcare providers confirming gestational age. Remember that this is an estimate — only about 5% of babies are born exactly on the due date.
The Formula
Naegele's rule assumes a standard 40-week (280-day) pregnancy counted from the first day of the last menstrual period — not from conception, because LMP is easier to date precisely. The cycle-length adjustment accounts for the fact that ovulation (and therefore conception) happens later in longer cycles, pushing the due date proportionally later. A woman with a 32-day cycle ovulates around day 18, so her due date falls 4 days later than the standard 28-day assumption.
Practical Examples
LMP January 1 with a 28-day cycle gives an estimated due date of October 8 the same year.
LMP February 14 with a 30-day cycle gives November 23 — two days later than the standard calculation, reflecting the longer cycle.
A pregnancy currently at 20 weeks marks the start of the second trimester and the halfway point.
The third trimester begins at 28 weeks (day 189 of pregnancy) — a key transition for medical appointments and delivery planning.
A pregnancy past 40 weeks (past due date) is called postterm; after 42 weeks, doctors usually recommend induction for safety.
Twin pregnancies are typically delivered 2–3 weeks earlier than singleton due dates, around 37–38 weeks, though the calculator still uses the standard 40-week estimate.