Gestational Age Calculator
Calculate gestational age in weeks and days from last menstrual period or ultrasound measurements. Gestational age determines fetal development milestones, test timing, and delivery planning.
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Key values and context for this tool: • Full Term: 37-42 Wks • Viability: 24 Weeks • Milestones: Weekly
Ready to run the numbers?
Why: This page explains what the Gestational Age calculator does, what to enter, and how to read the results—without repeating the overview above.
How: Enter your values in the calculator fields below, keep units consistent, then run the calculation to see results and any step-by-step work shown on this page.
Run the calculator when you are ready.
Sample Scenarios
🌱 Early First Trimester (8 weeks)
Newly pregnant, just had first ultrasound
👶 Viability Milestone (24 weeks)
Reaching the important viability threshold
✨ Full Term (39 weeks)
Ready for delivery any day now
📈 Mid Second Trimester (20 weeks)
Anatomy scan timing - halfway point
🧬 IVF Pregnancy (12 weeks)
Day 5 transfer, end of first trimester
📅 Long Cycle (35 days)
LMP with 35-day cycle adjustment
Method
LMP
Current
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
What is Gestational Age?
Gestational age measures pregnancy progress in weeks and days from the last menstrual period. Calculate from LMP, due date, ultrasound, or IVF transfer.
📅 Week-by-Week
Track exact weeks and days pregnant.
👶 Fetal Development
Size, weight, milestones by week.
🎯 Milestones
Viability, full term, key dates.
How is Gestational Age Calculated?
LMP: GA = Current Date - LMP. EDD: GA = 280 - Days Until EDD. Ultrasound: GA at scan + days since. IVF: Transfer date + (266 - embryo age).
Gestational vs Fetal Age
Gestational age is from LMP (40 weeks full term). Fetal age is from conception, typically 2 weeks less. At 12 weeks GA, baby is ~10 weeks fetal age.
Trimester Breakdown
First: Weeks 1-12. Second: 13-26. Third: 27-40. Each has distinct developmental milestones and care needs.
When to Check Gestational Age
Before prenatal visits, for screening timing (NIPT 10-13w, anatomy 18-22w, glucose 24-28w), and when planning maternity leave.
Key Milestones
Week 6: Heartbeat. Week 12: End 1st trimester. Week 20: Anatomy scan. Week 24: Viability. Week 28: 3rd trimester. Week 37: Early term. Week 40: Due date.
Term Categories
Preterm <37w. Early term 37-38w6d. Full term 39-40w6d. Late term 41-41w6d. Post-term ≥42w.
IVF Dating
IVF transfer dating is most accurate. Day 5 blastocyst: EDD = Transfer + 261 days. Day 3: +263. Day 6: +260.
Frequently Asked Questions
Why does gestational age start from LMP?
LMP is used because it is a date most women can reliably remember. The medical community uses LMP-based dating for consistency worldwide.
How accurate is gestational age calculation?
First trimester ultrasound dating (7-13 weeks) is most accurate, within 3-5 days. LMP-based dating can be off by 1-2 weeks for irregular cycles.
What is the difference between gestational age and fetal age?
Gestational age is from LMP (40 weeks full term). Fetal age is actual age from conception, typically 2 weeks less.
When is a pregnancy considered full term?
Full term is 39–40 weeks 6 days. Early term 37–38 weeks 6 days. Late term 41–41 weeks 6 days.
What is the viability milestone at 24 weeks?
At 24 weeks babies have a reasonable chance of survival if born early with NICU care. Survival rates vary by facility.
Can my due date change during pregnancy?
Your due date may be adjusted after early ultrasound if it differs from LMP. Once established in first trimester, it usually stays fixed.
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