Pregnancy Week Calculator
Enter your last menstrual period date to find your current pregnancy week.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Pregnancy Week Calculator
This calculator tells you exactly how many weeks and days pregnant you are based on your last menstrual period (LMP) date. Here is how to use it:
- Enter your LMP date. Select the first day of your last menstrual period using the date picker. This is the standard starting point used by all obstetric calculations, even though conception occurs about two weeks later.
- Read your results. The calculator instantly shows your gestational age in weeks and days, which trimester you are in, your estimated due date, how many days remain, and a brief milestone for your current week.
The calculator uses today's date automatically. Use Share to send your result, or Copy to save it.
About the Pregnancy Week Calculator
Gestational age is measured in weeks from the first day of the last menstrual period, not from conception. This means you are technically "2 weeks pregnant" at the time of conception. The full pregnancy is counted as 40 weeks (280 days) from LMP.
Trimesters divide the pregnancy into three roughly equal parts: the first trimester covers weeks 1-12, the second covers weeks 13-26, and the third begins at week 27 and continues through birth. Milestones shown are simplified summaries of typical fetal development at each week.
Frequently Asked Questions
Why does pregnancy start counting from LMP instead of conception?
The LMP date is used because it is a known, observable event, while the exact date of conception is rarely known with certainty. Ovulation and fertilization typically occur around day 14 of a 28-day cycle, about two weeks after the LMP. By convention, gestational age always starts from LMP, so conception actually occurs at approximately 2 weeks gestational age.
What is the difference between gestational age and fetal age?
Gestational age counts from the LMP and is the standard used in prenatal care. Fetal age (or conception age) counts from the moment of fertilization, which is about two weeks less than gestational age. When your doctor says you are 10 weeks pregnant, the fetus is approximately 8 weeks old. All due date and week calculators use gestational age by default.
What are the key pregnancy milestones by week?
Key milestones include: week 5 (heartbeat begins), week 12 (end of first trimester, risk of miscarriage drops), week 18-20 (anatomy ultrasound, baby may be felt moving), week 24 (viability milestone), week 28 (third trimester begins), week 37 (full term). Most prenatal appointments are scheduled around these milestones.
What if I don't know my LMP date?
If you do not know your LMP date, an early ultrasound (before 13 weeks) can establish gestational age by measuring the embryo's crown-rump length. This is considered more accurate than LMP dating when cycles are irregular. Your healthcare provider can also use a physical exam or other clinical signs to estimate how far along you are.