Estimate your pregnancy week, trimester, and due date from the first day of your last menstrual period.
How This Tracker Calculates Pregnancy Week
The tool counts forward from the first day of your last period and converts that number of days into gestational weeks and days. It also estimates your due date by adding 280 days to the LMP. This works best when your cycles are fairly regular and you are confident about the date you entered.
Why Doctors Count Pregnancy From LMP
Conception usually happens about two weeks after the start of the menstrual cycle, but the exact day is often uncertain. The LMP is a more reliable anchor date for many people, which is why pregnancy can feel "two weeks ahead" of what you expected at first. This is a normal feature of medical dating, not a sign that something is off.
When LMP Dating Becomes Less Reliable
LMP dating is less dependable if your cycles are irregular, you recently stopped hormonal contraception, you are breastfeeding, you are unsure of your dates, or you conceived through fertility treatment. In those situations, an early ultrasound or IVF treatment timeline usually gives a better official pregnancy date.
What Knowing Your Pregnancy Week Helps With
A pregnancy-week estimate helps you understand which trimester you are in, when certain symptoms are common, and how prenatal milestones are usually timed. It can also help you make sense of terms such as 6 weeks pregnant, 12 weeks pregnant, or 20-week anatomy scan. What it cannot do is confirm how the pregnancy is progressing or replace clinician review of symptoms and ultrasound findings.
When to Follow Your Clinician Instead
If your due date has already been confirmed by ultrasound or IVF treatment dates, that official timeline should override this tracker. Use the tool for orientation, but follow the pregnancy week and due date documented by your care team for appointments, scans, and decision-making.