Pregnancy Due Date Calculator

Calculate from Date Cycle length (days, only if LMP)

How due dates are calculated

The standard calculation is Naegele\'s rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP), assuming a 28-day cycle. This places conception at roughly day 14 of the cycle. About 70% of births occur within 10 days of the calculated due date.

Adjustments by calculation method

LMP-based: Most common. 280 days from first day of last period. Adjusted for cycle length variations.
Conception date: 266 days from confirmed conception. Most accurate if you tracked ovulation.
IVF day-3 transfer: 263 days from transfer date.
IVF day-5 transfer: 261 days from transfer date.
Ultrasound dating: Most accurate in the first trimester (6-12 weeks). Often used to adjust LMP-based dates when there\'s ambiguity.

Pregnancy timeline

First trimester (weeks 1-13): Major organs form. Highest miscarriage risk (10-20% of confirmed pregnancies before week 12). Morning sickness peaks at 9-11 weeks.
Second trimester (weeks 14-27): Often the easiest. Morning sickness eases, energy returns. First fetal movements (16-22 weeks). Anatomy scan at 18-22 weeks.
Third trimester (weeks 28-40): Major growth, increasing discomfort. Glucose screening at 24-28 weeks. Group B strep test at 35-37 weeks.

Key milestones

4 weeks: Missed period. Home pregnancy test detects.
6-8 weeks: First ultrasound (transvaginal). Heartbeat visible.
10-13 weeks: Nuchal translucency screening. NIPT blood test (chromosome screening).
18-22 weeks: Anatomy scan (detailed ultrasound). Often sex reveal.
24-28 weeks: Glucose tolerance test for gestational diabetes.
35-37 weeks: Group B strep swab.
37-42 weeks: Considered full term. Most births occur between 37-41 weeks. Past 42 weeks = post-term; induction is typically discussed.

Disclaimer

This calculator gives estimates, not medical advice. Real due dates depend on ovulation timing, embryo health, and ultrasound confirmations. Always work with your OB/midwife for accurate prenatal care.

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