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How to Calculate Your Pregnancy Week from LMP
Formula
Tracking pregnancy progress in weeks is the standard method used by obstetricians and midwives worldwide. Gestational age is calculated from the first day of the last menstrual period (LMP), not from conception, because the LMP date is typically more reliably known. A full-term pregnancy is approximately 280 days (40 weeks) from the LMP. This calculator converts your days since LMP into weeks, shows your trimester, and counts down to the estimated due date.
The pregnancy is divided into three trimesters: the first trimester covers weeks 1 through 13 (days 1-91), the second trimester spans weeks 14 through 27 (days 92-189), and the third trimester runs from week 28 through delivery at approximately week 40 (days 190-280). Each trimester brings different developmental milestones and medical check-up schedules. Knowing your exact week and trimester helps you follow prenatal care guidelines and understand your baby's developmental stage.
Common use cases:
- Tracking gestational age for prenatal care appointments
- Determining trimester for appropriate health guidelines
- Estimating the due date and remaining time until delivery
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