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Pregnancy Week Calculator
Gestational Age Calculator —
How Many Weeks Pregnant Am I?
Enter your Last Menstrual Period, conception date, ultrasound date, or IVF transfer date to instantly find out exactly how far along your pregnancy is. Get your trimester, baby’s development this week, due date, and upcoming prenatal milestones.
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40Weeks Tracked
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Choose the date you know most accurately
Your Gestational Age
Calculated from Week 1 Day 1 (first day of LMP)
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Weeks
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Days
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Trimester
Week 11st Trim.2nd Trim.3rd Trim.Week 40
Estimated Due Date
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Based on 280 days from LMP
Days Remaining
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Until estimated due date
Progress
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of pregnancy complete
Baby This Week
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Week --
Size: --
Weight: --
LMP / Pregnancy Start
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Conception Date (est.)
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Viability (Week 24)
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Full Term (Week 37)
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Upcoming Milestones
Gestational age is estimated from the first day of your Last Menstrual Period. Results assume a 28-day cycle and ovulation at day 14. Every pregnancy is unique — consult your obstetrician or midwife for confirmed dating and personalised care.
What is Gestational Age?
Gestational age is the standard medical measure of how far along a pregnancy is. It is counted in weeks and days from the first day of the mother’s Last Menstrual Period (LMP) — not from the date of conception.
This means that at the moment of conception (typically around day 14 of the cycle), a pregnancy is already considered to be 2 weeks along by gestational age. A full-term pregnancy lasts approximately 40 weeks (280 days) from LMP.
Clinical Standard
Gestational age is the universal measure used by obstetricians, midwives, and sonographers worldwide for all pregnancy dating, scan reporting, and milestone tracking.
Baby Development Guide
Each gestational week corresponds to a defined stage of fetal development — from neural tube formation in week 5 to lung maturation in week 36.
Appointment Scheduling
Prenatal scans, blood tests, and vaccinations are all scheduled relative to gestational age. Knowing your exact week is essential for timely antenatal care.
Preterm & Post-term Reference
Gestational age defines clinical thresholds: viability (< 24 weeks), premature (< 37 weeks), full term (37–42 weeks), and post-term (> 42 weeks).
Gestational Age vs. Fetal Age
These two terms are often confused but measure different things. Understanding the difference helps you interpret scan reports and medical communications accurately.
Gestational Age (GA)
Starts From
First day of Last Menstrual Period
Used by all doctors and scan reports
- Includes ~2 weeks before conception actually occurred
- A 12-week pregnancy by GA is ~10 weeks after conception
- Full term = 40 weeks GA (280 days from LMP)
- Reported on all ultrasound scans
Fetal Age (Embryonic / Conceptional Age)
Starts From
Date of Conception / Ovulation
Typically 2 weeks less than gestational age
- Reflects the actual age of the embryo or fetus
- A 12-week GA pregnancy has a fetal age of ~10 weeks
- Full term = ~38 weeks fetal age (266 days from conception)
- Used in IVF and embryology reports
Why LMP? Doctors use LMP because most women know their last period date reliably, whereas the exact conception date is rarely known. This makes LMP-based gestational age the most practical universal standard.
How Gestational Age is Determined
Healthcare providers use several methods to establish or confirm gestational age. The most accurate method depends on how early in pregnancy it is performed.
Last Menstrual Period (LMP)
The standard clinical method. Add 280 days (Naegele’s Rule) to the first day of the last period. Assumes a regular 28-day cycle with ovulation on day 14. Accurate for women with regular cycles.
First Trimester Ultrasound
Crown-Rump Length (CRL) measurement between weeks 8–13 is the most accurate method for dating — within ±3–5 days. Often used to confirm or correct LMP-based dating.
Second Trimester Ultrasound
Biometric measurements (head circumference, femur length, abdominal circumference) at the anatomy scan (week 18–22) give gestational age within ±10–14 days.
IVF Transfer Date
For IVF pregnancies, gestational age is calculated from the embryo transfer date plus the embryo’s age (Day 3, Day 5, or Day 6). Provides very accurate dating from the start.
Accuracy comparison: First trimester CRL ultrasound (±3–5 days) > LMP method (±7–10 days) > Second trimester scan (±10–14 days). If your ultrasound date differs from LMP by more than 7 days, your doctor will typically adjust to the ultrasound-based date.
Gestational Age by Trimester
Pregnancy is divided into three trimesters, each with distinct developmental stages, physical changes, and recommended care.
1
First Trimester
Weeks 1 – 13
- All major organs and systems form
- Heartbeat detectable from week 6
- Miscarriage risk highest (15–20%)
- Nausea, fatigue, and breast tenderness common
- First prenatal visit and NT scan (weeks 11–13)
2
Second Trimester
Weeks 14 – 27
- Miscarriage risk drops significantly
- Baby movements felt (quickening, weeks 18–22)
- Anatomy ultrasound at week 20
- Viability milestone reached at week 24
- Most women feel their best this trimester
3
Third Trimester
Weeks 28 – 40+
- Rapid weight gain and lung maturation
- Group B Strep test at week 35–37
- Full term from week 37
- Weekly OB visits from week 36
- Induction may be discussed after week 41
Baby Development Week by Week
A quick reference of fetal size, weight, and key milestones from Week 4 through Week 40.
| Week | Size | Weight | Key Milestone |
|---|---|---|---|
| 4 | Poppy seed (0.1 cm) | < 1 g | Implantation complete; hCG production begins |
| 6 | Lentil (0.6 cm) | < 1 g | Heartbeat begins; arm and leg buds appear |
| 8 | Kidney bean (1.6 cm) | 1 g | All major organs forming; embryo becomes a fetus |
| 10 | Strawberry (3.1 cm) | 4 g | Tiny fingernails forming; skeleton begins hardening |
| 12 | Lime (5.4 cm) | 14 g | Reflexes developing; kidneys producing urine |
| 14 | Lemon (8.7 cm) | 43 g | Unique fingerprints forming; sucking reflex present |
| 16 | Avocado (11.6 cm) | 100 g | Baby making facial expressions; ears in final position |
| 18 | Bell pepper (14.2 cm) | 190 g | Ears fully developed; can hear sounds outside womb |
| 20 | Banana (16.5 cm) | 300 g | Halfway point! Anatomy scan recommended |
| 22 | Papaya (27.8 cm) | 430 g | Eyebrows and eyelashes visible |
| 24 | Ear of corn (30 cm) | 600 g | Viability milestone; lungs begin producing surfactant |
| 27 | Cauliflower (36.6 cm) | 875 g | Eyes open for first time; brain activity increases |
| 28 | Large eggplant (37.6 cm) | 1,005 g | Third trimester begins; baby can blink and dream |
| 32 | Jicama (42.4 cm) | 1,702 g | Baby practising breathing; toenails complete |
| 34 | Cantaloupe (45 cm) | 2,146 g | Lungs nearly fully mature; CNS maturing rapidly |
| 37 | Swiss chard (48.6 cm) | 2,859 g | Full term — all organs ready for life outside womb |
| 40 | Watermelon (51.2 cm) | 3,462 g | Due date! Fully developed and ready to arrive |
Prenatal Appointments by Gestational Age
Each prenatal test and appointment is timed to a specific gestational age window. Missing these windows may reduce effectiveness or accuracy.
| Gestational Age | Appointment / Test | Purpose |
|---|---|---|
| 6 – 8 weeks | First prenatal visit | Confirm pregnancy, blood type, blood pressure baseline |
| 8 – 10 weeks | CVS (if indicated) | Chorionic villus sampling for chromosomal conditions |
| 11 – 13 weeks | NT scan + First trimester screen | Nuchal translucency; Down syndrome & trisomy risk |
| 15 – 20 weeks | Quad screen / AFP blood test | Neural tube defects and chromosomal conditions |
| 18 – 22 weeks | Anatomy (Level 2) ultrasound | Detailed organ and structure assessment; gender |
| 24 – 28 weeks | Glucose tolerance test (GCT/GTT) | Screen for gestational diabetes |
| 28 weeks | RhoGAM injection (if Rh−) | Prevent Rh sensitisation |
| 28 weeks | Tdap vaccination | Protect newborn from whooping cough |
| 35 – 37 weeks | Group B Streptococcus (GBS) swab | Determine need for IV antibiotics during labour |
| 36+ weeks | Weekly OB visits | Monitor position, cervical ripening, fetal movement |
| 40+ weeks | Non-stress test / BPP | Monitor fetal well-being if overdue |
Important: This schedule reflects general guidelines. Your doctor may recommend additional or different appointments based on your personal health history, risk factors, and local healthcare protocols.
Frequently Asked Questions
Common questions about gestational age and pregnancy dating.
Gestational age is counted from the first day of the Last Menstrual Period (LMP) because most women know this date reliably, whereas the exact moment of conception is rarely known. Since ovulation and conception typically occur around day 14 of the cycle, gestational age is approximately 2 weeks ahead of the actual age of the embryo. This is an internationally agreed clinical convention.
LMP-based dating is accurate to within ±7–10 days for women with regular 28-day cycles. If your cycle is irregular, shorter, or longer than 28 days, LMP dating may be less precise. A first-trimester ultrasound measuring Crown-Rump Length (CRL) is accurate to ±3–5 days and is the gold standard. If your ultrasound dates differ from LMP by more than one week, your provider will typically revise your dates to match the scan.
Gestational age is measured from the LMP and is the standard medical measure (e.g., "24 weeks pregnant"). Fetal age (also called embryonic age or conceptional age) is measured from the date of conception and is approximately 2 weeks less than gestational age. So a pregnancy at 24 weeks gestational age has a fetal age of about 22 weeks. Most parenting apps and doctors quote gestational age.
Viability refers to the gestational age at which a baby has a reasonable chance of surviving outside the womb with medical support. Week 24 (168 days gestational age) is the widely used threshold, at which survival rates are approximately 50%. Survival rates improve significantly with each additional week: ~85% at 26 weeks and ~90–95% at 28 weeks. Below 22–23 weeks, survival is extremely unlikely even with intensive care.
Yes. If you know your conception or ovulation date, add 14 days to get the equivalent LMP date, then calculate as usual. If you have an ultrasound report showing gestational age at a specific scan date, use the Ultrasound method in this calculator. For IVF pregnancies, use the embryo transfer date with the embryo's age (Day 3, 5, or 6).
Full term pregnancy is defined as 37 completed weeks (259 days) to 41 weeks and 6 days of gestational age. The American College of Obstetricians and Gynecologists (ACOG) further classifies: Early Term (37–38 weeks), Full Term (39–40 weeks), Late Term (41 weeks), and Post Term (42+ weeks). Babies born at 37–38 weeks have a slightly higher risk of breathing difficulties and feeding problems than those born at 39–40 weeks.
For IVF, gestational age is calculated by working backwards from the embryo transfer date. Subtract the embryo's age at transfer (Day 3, Day 5, or Day 6) to get the equivalent fertilisation/conception date, then add 14 days to get the equivalent LMP. For a Day-5 blastocyst transfer, subtract 5 days from the transfer date to get conception date, then add 14 days for the LMP equivalent. The due date is 280 days from that LMP equivalent.
Conclusion
Knowing your gestational age is one of the most important pieces of information throughout pregnancy. It determines which prenatal tests are relevant, when to schedule appointments, how to interpret ultrasound reports, and when to expect key developmental milestones for your baby.
While this calculator provides accurate estimates based on your inputs, always have your gestational age confirmed by your obstetrician or midwife — especially if your cycles are irregular or you are unsure of your LMP date. A first-trimester ultrasound remains the gold standard for precise dating.
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