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Find your precise gestational age in weeks and days and check baby development milestones.
Our pregnancy algorithms, trimester calculations, and health insights are constructed based on peer-reviewed clinical guidelines and approved by certified medical practitioners.
Calculations adhere to standard clinical guidelines set by the American College of Obstetricians and Gynecologists.
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Medical resources are written and periodically updated by an expert board of OB-GYNs and child care advisors.
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When you visit your obstetrician, the primary metric they use to evaluate your pregnancy is your gestational age. This is the official age of your pregnancy in weeks and days. It dictates everything from when scans are performed to whether baby weight is on track. Knowing how to calculate and interpret your gestational age is key to participating in your prenatal care.
This article details how gestational age is calculated, why it differs from fetal age, and how it guides medical checkups throughout your pregnancy.
Gestational age is calculated based on the first day of your Last Menstrual Period (LMP). To calculate your gestational age today:
For example, if 73 days have elapsed since your last period: 73 divided by 7 is 10 with a remainder of 3. Your gestational age is 10 weeks and 3 days. Our calculator widget above does this math automatically, adjusting for cycle variations.
It is important to understand that gestational age does not measure the actual age of the baby. Instead, it measures the age of the pregnancy cycle. The baby's actual biological age is called fetal age or conception age:
| Feature | Gestational Age | Fetal (Conception) Age |
|---|---|---|
| Starting Point | First day of last menstrual period (LMP) | Date of conception/fertilization |
| Duration | Standard 40 weeks (280 days) | Standard 38 weeks (266 days) |
| Who Uses It | Obstetricians, midwives, medical records | Researchers, developmental biologists |
| Difference | Always roughly 2 weeks longer | Always roughly 2 weeks shorter |
Because the exact day of ovulation is variable, medical professionals standardize care on gestational age to maintain a consistent baseline.
Your gestational age determines when you will receive key prenatal screenings and procedures:
Monitoring your gestational progress is easy with our Gynosakhi companion application. Get daily updates on your baby's development, track your maternal symptoms, log doctor appointments, and consult our 24/7 AI chatbot for any health questions. Download Gynosakhi on iOS and Android today.
Clinical Disclaimer: The calculations, timelines, and guides provided on this page are for educational and planning purposes only. They are based on clinical standards from ACOG, but do not replace professional medical advice, diagnosis, or clinical ultrasound assessments from your OB-GYN.
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Medical answers to standard queries regarding pregnancy calculations, due dates, and trimester guidelines.
Gestational age is the measure of how far along your pregnancy is in weeks and days, calculated from the first day of your last menstrual period (LMP).
While LMP calculates gestational age, it is verified or adjusted during your first-trimester ultrasound. The crown-rump length (CRL) of the fetus is measured, providing a highly accurate biological age.
By clinical convention, gestational age starts on the first day of your last period. Because ovulation and conception occur roughly two weeks later, you are technically not pregnant during the first two weeks of your gestational age.
Count the total number of days elapsed since the start of your last period (LMP). Divide by 7. The quotient is your gestational weeks, and the remainder is your days (e.g., 73 days divided by 7 is 10 weeks and 3 days).
LMP-based calculations assume a regular 28-day cycle with ovulation on day 14. If you have an irregular cycle or irregular ovulation, the calculation can be off by a week or more. Ultrasound scans are used to verify the timeline.
Gestational age is measured from the LMP (standard obstetric timeline, 40 weeks total). Conceptional age (fetal age) is the biological age of the baby starting from fertilization, which is almost always 2 weeks shorter (38 weeks total).
CRL is the measurement of the embryo from the top of the head (crown) to the bottom of the buttocks (rump), taken during a first-trimester ultrasound. In early pregnancy, embryos grow at a highly uniform rate, making CRL the most accurate biological dating method.
Your gestational age timeline can be adjusted during the first trimester if early ultrasound measurements differ from your LMP dates by more than 7 days. Once adjusted, it remains fixed; late-pregnancy scans do not change your gestational age baseline.
Calendar months vary in length (28 to 31 days) making them too inconsistent for clinical timelines. Weeks and days are uniform (always 7 days) and align directly with critical developmental milestones and screening windows.
Standard gestational calculations assume ovulation on day 14 of a 28-day cycle. If you have a longer cycle (e.g., 35 days), ovulation occurred later (around day 21). Our calculator adjusts for this, shifting your gestational age to match your cycle profile.
