Pregnancy Calendar Week-by-Week
Calculate your pregnancy timeline week-by-week with baby size milestones, trimester boundaries, and key prenatal screening appointments from LMP or due date.
- American College of Obstetricians and Gynecologists data · June 2026
- Edited by Martín Rodríguez
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Data updated: · Source: American College of Obstetricians and Gynecologists (ACOG) – Methods for Estimating Due Date
Edited by: Martín Rodríguez (editorial policy )
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Estimated Due Date (EDD)
Estimated due date October 21, 2026 from a January 15 LMP. Estimates only; confirm with your provider.
Current Gestational Week
Current Trimester
Baby Size Comparison
Weeks Until Due Date
Week-by-Week Calendar
Key Prenatal Appointments
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See period-by-period detail
General information. For health, fertility or parenting decisions consult licensed professionals.
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How to use this calculator
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Track your pregnancy from your last period through delivery with a complete week-by-week calendar. Enter your last menstrual period (LMP) or your due date to instantly generate your estimated delivery date, current gestational week, trimester, baby size comparison, weeks remaining, and a full prenatal appointment schedule. All dates follow standard obstetric conventions: 280 days (40 weeks) from LMP, as defined by ACOG and the WHO.
When to use this calculator
- You just got a positive test and want to know your due date and how far along you already are based on your last period.
- You know your ultrasound due date and want to work backward to see what your LMP-equivalent week would be.
- You're planning maternity leave and need to know exactly when week 36 falls so you can schedule your last day.
- Your OB mentioned the anatomy ultrasound is at 18–22 weeks and you want a real calendar date to book the appointment.
- You want to share weekly baby size updates with your partner or family and need the exact fruit comparison for each week.
- You're preparing a hospital bag checklist and want to know when full term (week 37) begins.
Fetal Size Milestones by Gestational Week
| Week | Size comparison | Crown-rump length | Estimated weight |
|---|---|---|---|
| 8 | Raspberry | 1.6 cm | < 1 g |
| 12 | Poppy seed | 5.4 cm | 14 g |
| 16 | Avocado | 11.6 cm | 100 g |
| 20 | Banana | 16.4 cm | 300 g |
| 24 | Corn on the cob | 20 cm | 600 g |
| 28 | Eggplant | 25 cm | 1.0 kg |
| 32 | Squash | 28 cm | 1.7 kg |
| 36 | Romaine lettuce | 32 cm | 2.6 kg |
| 40 | Watermelon | 36 cm | 3.4 kg |
Fuente: ACOG / WHO — standard obstetric reference values (2023–2024)
How it works
How it works
This calculator uses standard obstetric dating: pregnancy is counted from the first day of the last menstrual period (LMP), not from conception. Even though fertilization occurs roughly 2 weeks after LMP, dating from LMP is universal because the exact day of ovulation is rarely known.
LMP (Day 0) → Conception (~Day 14) → Due Date (Day 280 = Week 40)If you enter a due date instead, the calculator simply works backward: LMP = due date − 280 days, then regenerates the full calendar from that LMP.
Trimester boundaries
| Trimester | Gestational weeks | Days from LMP |
|---|---|---|
| First | 1–13 | 1–91 |
| Second | 14–27 | 92–189 |
| Third | 28–40+ | 190–280+ |
Baby size milestones
The formula picks the closest week from a reference table and returns both the food comparison and clinical measurements (crown-rump length and estimated fetal weight):
Key prenatal appointment schedule
The calculator also generates dated appointment windows based on standard ACOG recommendations:
| Window | Appointment |
|---|---|
| Weeks 8–10 | Dating ultrasound, confirm viability, initial bloodwork |
| Weeks 11–13 | Nuchal translucency (NT) scan — screens for chromosomal abnormalities |
| Weeks 15–20 | Quad screen / integrated first + second trimester screening |
| Weeks 18–22 | Anatomy ultrasound — fetal organs, sex determination, placenta position |
| Weeks 24–28 | Gestational diabetes screening (1-hour glucose challenge test) |
| Weeks 28–34 | RhoGAM injection (if Rh-negative), repeat CBC and antibody screen |
| Weeks 35–37 | Group B Streptococcus (GBS) vaginal/rectal swab |
| Weeks 36–40 | Biweekly then weekly visits; cervical exams; NST if post-term |
Worked example
Input: LMP = January 15, 2026 (calculate-from: LMP)
Limitations
Example: LMP on January 15, 2026
Due date: LMP + 280 days (40 weeks) = October 21, 2026
Trimester boundaries: weeks 1–13 first, 14–27 second, 28+ third
Key appointments: NT scan ~April 1, anatomy ultrasound ~May 20, GBS swab ~mid-September
Estimated due date October 21, 2026 from a January 15 LMP. Estimates only; confirm with your provider.
Disclaimer: Results are indicative and do not replace personalized guidance. Before making decisions that matter, consult a licensed professional in the relevant field.
Frequently asked questions
What is the LMP and why is pregnancy dated from it?
LMP stands for Last Menstrual Period — the first day of your most recent period before becoming pregnant. Obstetricians date pregnancy from LMP because the exact day of ovulation and fertilization is rarely known, while the start of a period is. By convention, pregnancy is 280 days (40 weeks) from LMP, even though the embryo is only about 38 weeks old at birth.
How accurate is the estimated due date?
Only about 5% of babies are born on the exact due date. Roughly 80% deliver within 2 weeks on either side. First-trimester ultrasound (before 14 weeks) is accurate to ±3–5 days and is the gold standard for setting your EDD if the LMP-based date and ultrasound differ by more than 5–7 days.
What should I do if my cycle is irregular?
If your cycles are shorter than 21 days or longer than 35 days, LMP dating will be off. Ask your provider for a first-trimester dating ultrasound (ideally before 13 weeks 6 days), which measures the fetal crown-rump length (CRL) to calculate gestational age independently of your cycle.
Why is the NT scan so time-sensitive (11–13 weeks)?
The nuchal translucency ultrasound measures fluid at the back of the fetal neck, which naturally increases after 14 weeks, making the measurement unreliable. It must be done between 11 weeks 0 days and 13 weeks 6 days. Combined with bloodwork (PAPP-A + free beta-hCG), it detects Down syndrome (Trisomy 21) and Trisomy 18 with approximately 85% sensitivity.
What happens at the 20-week anatomy ultrasound?
Also called the fetal anomaly scan or TIFFA (Targeted Imaging for Fetal Anomalies), this ultrasound at 18–22 weeks evaluates: fetal brain, heart (4 chambers), spine, kidneys, stomach, limbs, abdominal wall, and placenta position. It can also reveal fetal sex if you choose to find out. Most structural abnormalities, if present, are identified here.
What is the gestational diabetes test and who needs it?
At 24–28 weeks, placental hormones peak and insulin resistance increases. A 1-hour glucose challenge test (50 g glucose drink) screens for gestational diabetes. If the result is ≥140 mg/dL (or ≥130 mg/dL per some protocols), a 3-hour glucose tolerance test follows for diagnosis. ACOG recommends universal screening regardless of risk factors.
What is Group B Strep and why is testing at 35–37 weeks?
Group B Streptococcus (GBS) is a bacterium present in the vaginal/rectal flora of about 25% of healthy pregnant women without causing symptoms. However, it can infect the newborn during delivery, causing sepsis, pneumonia, or meningitis. Testing at 35–37 weeks (a vaginal/rectal swab) identifies carriers who need IV penicillin during labor. Earlier testing isn't reliable because GBS status can change.
What does 'full term' mean exactly?
ACOG revised terminology in 2013: 37 weeks 0 days marks the start of 'early term' (37–38 weeks 6 days). Full term is 39 weeks 0 days to 40 weeks 6 days. Late term is 41 weeks 0 days to 41 weeks 6 days, and post-term is 42 weeks and beyond. This distinction matters because outcomes are best in the full-term window — elective delivery before 39 weeks without a medical indication is not recommended.
Can I use this calculator if I had IVF?
Not directly from LMP. For IVF, your reproductive endocrinologist calculates the EDD from the embryo transfer date: for a day-5 blastocyst transfer, add 261 days to the transfer date (equivalent to 37 weeks 2 days from the LMP equivalent). Use the 'Due Date' input on this calculator and enter the date your clinic gave you to get the rest of the timeline.
How do I count gestational weeks — is week 1 actually day 1?
Gestational age is stated as completed weeks. You are 'in week 8' from days 49–55 after LMP (7 weeks and 1–6 days completed). Your provider may write it as '7+3' meaning 7 weeks and 3 days. Week 40 day 0 is the due date. After the due date, you enter week 41, then week 42 (post-term).
Sources & references
- ACOG Practice Bulletin No. 700 – Methods for Estimating Due Date — American College of Obstetricians and Gynecologists (2017)
- ACOG Gestational Age Assessment — ACOG (2023)
- WHO Recommendations on Antenatal Care for a Positive Pregnancy Experience — World Health Organization (2016)
- CDC – Pregnancy: Prenatal Care — Centers for Disease Control and Prevention (2024)
- NICHD – Prenatal Care and Tests — National Institute of Child Health and Human Development (2024)
Methodology & trust
Editorial
familia calculator reviewed by Martín Rodríguez, editor of Hacé Cuentas, checked against ACOG Practice Bulletin No. 700 – Methods for Estimating Due Date, following our editorial policy and methodology.
Updates
Last reviewed: June 2026. Parameters are verified periodically against the cited sources.
Privacy
Calculations run 100% in your browser. We do not store or transmit your data.
Limitations
Indicative results. For critical decisions, consult a professional.
📌 How to cite this calculator
Rodríguez, M. (2026). Pregnancy Calendar Week-by-Week. Hacé Cuentas. https://hacecuentas.com/en/pregnancy-calendar-week-by-week
Content licensed under CC-BY 4.0 — reuse it citing the source with a link to Hacé Cuentas.