Pregnancy Calculator: How Far Along Are You?

Calculating Gestational Age

Pregnancy dating starts from the first day of the last menstrual period (LMP), not conception. This is because LMP is observable; conception timing is often uncertain.

Example

If conception occurred ~November 25 (ovulation), LMP ≈ November 11. By December 19, gestational age = 5 weeks 6 days (≈40 days from LMP), commonly called "4 weeks pregnant" in clinical parlance (completed weeks).

Standard Pregnancy Length

• Full term: 40 weeks (280 days) from LMP.
• Trimesters: 1–13 weeks, 14–26 weeks, 27–40 weeks.
• Due date (Naegele's rule): LMP + 7 days – 3 months + 1 year.

Ultrasound Dating

Early ultrasound (crown-rump length, 7–13 weeks) is more accurate than LMP if cycles are irregular. It may adjust the due date.