Calculate your current gestational age in weeks and days based on your last menstrual period (LMP), conception date, or ultrasound measurements. Track pregnancy milestones, estimated due date, and trimester information.
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📊 Calculate Your Gestational Age
Standard is 28 days. Range: 21–45 days.
Conception typically occurs around ovulation day.
CRL measured in millimeters. Typical range: 2–120 mm.
Current Gestational Age
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weeks + days pregnant
Estimated Due Date (EDD)
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40 weeks from LMP
Current Trimester
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Pregnancy stage
Days Remaining
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until estimated due date
Weeks Remaining
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weeks until due date
Percentage Complete
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of 40-week pregnancy
📝 Calculation Details
🎯 Important Pregnancy Milestones
📆 Due Date Information
Estimated Due Date (EDD)
—
40 weeks from LMP
Conception Window
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Estimated conception date
First Trimester Ends
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Week 13 complete
Second Trimester Ends
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Week 27 complete
Full Term Range
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37 weeks to 42 weeks
Early Term (37-38 wks)
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Early term start date
📝 About Your Due Date
📋 Real-World Gestational Age Examples
📅 Example 1: LMP-Based Calculation
A woman has her last menstrual period on January 15, 2026, with a regular 28-day cycle.
Gestational Age on June 3, 2026:~20 weeks
Estimated Due Date:October 22, 2026
Trimester: Second trimester (weeks 14-27)
Calculation: From January 15 to June 3 is approximately 20 weeks. EDD is January 15 + 280 days = October 22, 2026.
This is the standard Naegele's rule calculation used by most healthcare providers.
💕 Example 2: Conception Date Calculation
A woman knows her conception date was March 1, 2026.
Gestational Age on June 3, 2026:~16 weeks
Estimated Due Date:November 22, 2026
Conception date + 266 days = due date. Gestational age adds ~2 weeks to account for LMP dating convention.
🔬 Example 3: Ultrasound (CRL) Dating
An ultrasound at 12 weeks measures a CRL of 55 mm.
Corresponding Gestational Age:~12 weeks + 1 day
First-trimester ultrasound dating is the gold standard. The formula CRL (mm) + 42 estimates gestational age in days for early pregnancy.
🎯 Example 4: Trimester Determination
A woman is 25 weeks pregnant.
Trimester:Second Trimester
She has completed about 62.5% of her pregnancy with approximately 15 weeks remaining.
📊 Example 5: Early Pregnancy Dating
A woman with LMP of April 20, 2026 on June 3, 2026.
Gestational Age:~6 weeks + 2 days
Estimated Due Date:January 25, 2027
At 6 weeks, an early ultrasound may detect a fetal heartbeat. First trimester.
📖 How to Calculate Gestational Age
📅 Method 1: LMP Date
Enter the first day of your last menstrual period. This is the most common method. Gestational age is measured from this date, totaling ~40 weeks (280 days) for full-term.
💕 Method 2: Conception Date
If you know the exact conception date (typically ovulation + 24 hours), enter it here. GA = conception date + 266 days + 14 days adjustment.
🔬 Method 3: Ultrasound (CRL)
Enter the ultrasound date and Crown-Rump Length (CRL) in mm. Most accurate between 7-14 weeks. GA estimated from fetal size.
🎯 Why Accuracy Matters
Accurate dating is crucial for monitoring development, scheduling screenings (NT at 11-14 weeks), and managing preterm or post-term pregnancies.
Naegele's Rule: EDD = LMP Date + 280 Days (40 Weeks)
This is the standard formula used to calculate estimated due date from the last menstrual period.
Conception Method: EDD = Conception Date + 266 Days (38 Weeks)
Since conception occurs ~2 weeks after LMP, add 266 days to the conception date.
Gestational age is the number of weeks and days a pregnancy has progressed, measured from the first day of the woman's last menstrual period (LMP) to the current date. It is the standard method used by healthcare providers worldwide to date pregnancies, schedule prenatal testing, and track fetal development. A full-term pregnancy is approximately 40 weeks (280 days) from LMP, divided into three trimesters.
Gestational Age vs. Fetal Age
Gestational age is measured from LMP (~40 weeks at full term), while fetal age (conceptual age) is measured from conception, which occurs ~2 weeks after LMP. Fetal age is usually gestational age minus 2 weeks. Healthcare providers typically use gestational age because LMP dates are easier to determine.
Understanding Pregnancy Trimesters
Pregnancy is divided into three trimesters, each approximately 13-14 weeks long. The first trimester (weeks 1-13) involves rapid organ development and early screening. The second trimester (weeks 14-27) is often called the "golden period" with fetal movements and anatomy scan. The third trimester (weeks 28-40+) involves lung maturation, rapid growth, and labor preparation.
Frequently Asked Questions
What is gestational age and how is it calculated?
Gestational age is the number of weeks and days a pregnancy has progressed, measured from the first day of the last menstrual period (LMP). It can also be calculated from conception date (typically 2 weeks after LMP) or estimated via ultrasound CRL measurements. A full-term pregnancy is approximately 40 weeks (280 days) from LMP.
How accurate is ultrasound for dating gestational age?
First-trimester ultrasound (especially between 11-14 weeks) is the most accurate method, with an accuracy of ±5-7 days. Crown-rump length (CRL) is the gold standard. Second-trimester ultrasound has accuracy of ±7-10 days, while third-trimester dating is less precise at ±14-21 days.
What is the difference between gestational age and fetal age?
Gestational age is measured from LMP (~40 weeks at full term). Fetal age (conceptual age) is measured from conception, ~2 weeks after LMP. So fetal age is gestational age minus 2 weeks. Healthcare providers use gestational age for consistency.
When does each trimester start and end?
First Trimester: Week 1-13 — Rapid organ development, implantation, heartbeat detection, NT screening.
Third Trimester: Week 28 to delivery — Lung maturation, rapid weight gain, labor preparation.
What is the estimated due date based on LMP?
The EDD is calculated by adding 280 days (40 weeks) to the LMP. This is Naegele's rule. Only about 5% of babies are born exactly on their due date. Full-term ranges from 37 to 42 weeks. Due dates may be adjusted if first-trimester ultrasound shows significant discrepancy.
Can I calculate gestational age after 20 weeks?
Yes, but the most accurate dating is done in the first trimester. After 20 weeks, ultrasound measurements are less precise (±14-21 days). LMP-based dating remains valid if cycles are regular. An early dating ultrasound provides the best accuracy.
How do I calculate my due date with an irregular cycle?
Our calculator allows you to adjust the cycle length (21-45 days). For longer cycles, ovulation occurs later and the due date adjusts forward. For shorter cycles, the due date adjusts earlier. First-trimester ultrasound is especially recommended for accurate dating with irregular cycles.
What is CRL (Crown-Rump Length) and how is it used?
Crown-Rump Length (CRL) measures the fetus from head to buttocks via ultrasound. It is the most accurate single measurement for first-trimester dating (7-14 weeks). GA is estimated as CRL (mm) + 42 days. A CRL of 10 mm ≈ 7 weeks + 1 day; 60 mm ≈ 12 weeks + 3 days.
⚠️ Medical Disclaimer: This calculator is for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your pregnancy or due date. Ultrasound dating by a trained professional is the gold standard for determining gestational age.