Pregnancy Due Date Calculator
Calculate your baby's due date and track your pregnancy
About the Calculator
Your due date is one of the first things you want to know - and one of the first things your provider will confirm. This calculator estimates it four ways: from your last menstrual period (standard clinical method), conception or ovulation date, an ultrasound measurement, or IVF transfer date. The most accurate due date comes from combining the strongest data you have. The week-by-week guide below explains what is happening with your baby and your body at each stage, so you can orient yourself, plan appointments, and know what to expect. Use the Pregnancy Due Date Calculator to get a clear result you can act on right away.
Pregnancy week-by-week guide
First trimester (1–13)
Second trimester (14–27)
Third trimester (28–42)
Pregnancy week-by-week: full reference
| Week | Baby size | Baby's development | You might experience |
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| 1 | not yet conceived 🗓️ |
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| 2 | not yet conceived 🗓️ |
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| 3 | blastocyst (smaller than a grain of sand) •about 0.1 mm |
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| 4 | poppy seed 🌱about 1 mm |
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| 5 | sesame seed ⚪3 mm |
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| 6 | lentil 🫘5-6 mm |
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| 7 | blueberry 🫐10 mm |
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| 8 | raspberry 🍇16 mm |
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| 9 | grape 🍇23 mm |
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| 10 | strawberry 🍓1.2 in (3.1 cm) · 0.14 oz (4 g) |
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| 11 | lime 🍋1.6 in (4.1 cm) · 0.25 oz (7 g) |
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| 12 | plum 🍑2.1 in (5.4 cm) · 0.5 oz (14 g) |
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| 13 | peach 🍑2.9 in (7.4 cm) · 0.8 oz (23 g) |
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| 14 | lemon 🍋3.4 in (8.7 cm) · 1.5 oz (43 g) |
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| 15 | apple 🍎4 in (10.1 cm) · 2.5 oz (70 g) |
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| 16 | avocado 🥑4.6 in (11.6 cm) · 3.5 oz (100 g) |
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| 17 | pear 🍐5.1 in (13 cm) · 5 oz (140 g) |
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| 18 | sweet potato 🍠5.6 in (14.2 cm) · 6.7 oz (190 g) |
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| 19 | mango 🥭6 in (15.3 cm) · 8.5 oz (240 g) |
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| 20 | banana 🍌6.5 in (16.4 cm) · 10.6 oz (300 g) |
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| 21 | carrot 🥕7 in (17.8 cm) · 12.7 oz (360 g) |
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| 22 | papaya 🥭7.6 in (19.3 cm) · 15.2 oz (430 g) |
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| 23 | large mango 🥭8 in (20.3 cm) · 1.1 lb (500 g) |
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| 24 | corn 🌽8.5 in (21.6 cm) · 1.3 lb (600 g) |
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| 25 | rutabaga 🥬9 in (22.9 cm) · 1.5 lb (660 g) |
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| 26 | lettuce 🥬9.4 in (23.9 cm) · 1.7 lb (760 g) |
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| 27 | cauliflower 🥦9.6 in (24.5 cm) · 2 lb (900 g) |
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| 28 | eggplant 🍆10 in (25.4 cm) · 2.2 lb (1 kg) |
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| 29 | butternut squash 🎃10.5 in (26.7 cm) · 2.5 lb (1.2 kg) |
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| 30 | cabbage 🥬10.8 in (27.5 cm) · 3 lb (1.4 kg) |
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| 31 | coconut 🥥11.2 in (28.5 cm) · 3.3 lb (1.5 kg) |
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| 32 | jicama 🥔11.5 in (29.3 cm) · 3.8 lb (1.7 kg) |
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| 33 | pineapple 🍍11.8 in (30 cm) · 4.2 lb (1.9 kg) |
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| 34 | cantaloupe 🍈12 in (30.5 cm) · 4.7 lb (2.1 kg) |
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| 35 | honeydew 🍈12.3 in (31.3 cm) · 5.3 lb (2.4 kg) |
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| 36 | papaya 🥭12.6 in (32 cm) · 5.8 lb (2.6 kg) |
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| 37 | swiss chard 🥬13 in (33 cm) · 6.3 lb (2.9 kg) |
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| 38 | leek 🧅13.2 in (33.5 cm) · 6.8 lb (3.1 kg) |
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| 39 | mini watermelon 🍉13.4 in (34 cm) · 7.3 lb (3.3 kg) |
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| 40 | watermelon 🍉14 in (35.6 cm) · 7.5 lb (3.4 kg) |
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| 41 | watermelon 🍉14.2 in (36 cm) · 7.9 lb (3.6 kg) |
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| 42 | watermelon 🍉14.4 in (36.6 cm) · 8.1 lb (3.7 kg) |
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Important
This calculator provides estimates only and should not replace medical advice. Only about 5% of babies are born on their exact due date. Your healthcare provider will confirm your due date. Ultrasound dating (especially first trimester) is most accurate. If you have irregular cycles, LMP-based calculations may be less accurate. This tool is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
The Formula
Understanding your due date
Gestational age vs. fetal age
Gestational age - the clinical standard - counts from the first day of your last menstrual period, not from conception. That means at conception you are already considered about 2 weeks pregnant by gestational age. By week 4, when many home tests first turn positive, developmental age is closer to 2 weeks. Providers use gestational weeks for all clinical dating and milestones.
What "full term" actually means
ACOG now separates term pregnancy into clinically meaningful categories:
- Early term: 37 weeks 0 days through 38 weeks 6 days
- Full term: 39 weeks 0 days through 40 weeks 6 days
- Late term: 41 weeks 0 days through 41 weeks 6 days
- Post term: 42 weeks 0 days and beyond
Babies born at 39-40 weeks have the best outcomes on average. Early-term babies (37-38 weeks) may still face higher risk of breathing and feeding challenges.
The 280-day rule (Naegele's Rule)
Standard LMP dating adds 280 days (40 weeks) to the first day of your last menstrual period. This 19th-century framework assumes a 28-day cycle with ovulation around day 14. If your cycle is consistently longer, shorter, or irregular, your true conception timing shifts and your real due date may move by days to weeks.
FAQ
How accurate is my due date?
LMP-based due dates are generally accurate within about 2 weeks for people with regular 28-day cycles, and only about 5% of babies arrive on the exact date. First-trimester ultrasound (8-13 weeks, crown-rump length) is usually the most accurate dating method and is commonly accurate within 5-7 days. Your provider may adjust your due date based on ultrasound at your first prenatal visit.
What is the difference between gestational age and fetal age?
Gestational age counts from the first day of your last menstrual period and is the standard used in clinical care. Fetal (or conception) age counts from actual fertilization, typically about 2 weeks later. A pregnancy described as 6 weeks gestational age usually corresponds to about 4 weeks of embryonic development.
What if my cycle is not 28 days?
LMP dating assumes ovulation around day 14 of a 28-day cycle. If your cycle is longer, conception often happens later and your due date may shift later; shorter cycles can shift conception earlier. The cycle length field in this calculator adjusts for that. With very irregular cycles, early ultrasound tends to be more reliable than LMP-only dating.
What is a full-term pregnancy?
ACOG defines full term as 39 weeks 0 days through 40 weeks 6 days. Early term is 37-38 weeks, late term is 41 weeks, and post term is 42+ weeks. While many babies born at 37-38 weeks do well, outcomes are best on average in the 39-40 week window.
What is the difference between an IVF due date and a natural pregnancy due date?
IVF dating is usually more precise because fertilization timing is known. For a Day 5 transfer, due date calculation adds 261 days to transfer date; for Day 3 transfer, 263 days. This reflects embryo age at transfer and maps it to standard 40-week gestational dating.
When should I call my doctor if I'm past my due date?
Many providers schedule additional monitoring by 41 weeks, including fetal surveillance and amniotic fluid checks. Induction is commonly discussed between 41 and 42 weeks, and sometimes earlier depending on clinical context. If you notice decreased fetal movement at any point after viability, contact your provider promptly rather than waiting.
Can stress or diet affect my due date?
They do not change the calculated due date itself, which is based on conception timing. However, chronic severe stress, poor nutrition, smoking, and certain medical conditions are associated with higher risk of preterm birth. Good prenatal care, adequate nutrition (including folate early), and avoiding smoking and alcohol support healthier outcomes.
Tips & Strategies
Treat your due date as a range, not a deadline. Only about 5% of babies are born on the exact estimated date. Most full-term births happen between 38 and 42 weeks, so your due date works best as the center of a 4-week arrival window.
First-trimester ultrasound is usually the best dating anchor. Crown-rump length measured around weeks 8-13 is typically accurate within about 5-7 days. After 20 weeks, ultrasound dating becomes less precise because fetal growth rates diverge more.
Provider confirmation is part of the process. This calculator gives a clinically sound estimate, but your provider also uses cycle history, ultrasound findings, and medical context to finalize dating. LMP assumes a 28-day cycle and ovulation near day 14.
Irregular cycles make LMP-only estimates less reliable. If your cycles vary significantly or you have irregular ovulation (including with PCOS), LMP-based dating can differ from ultrasound estimates by 1-2 weeks. Early ultrasound is especially valuable in these cases.
IVF pregnancies use embryo-age-specific dating. IVF due dates are calculated from known embryo development timing, not transfer date alone. Day 5 transfer and Day 3 transfer use different offsets, and this calculator accounts for that distinction.
Things Worth Knowing
- •Naegele's Rule is over 200 years old and still the global baseline: adding 280 days to LMP remains the standard clinical framework despite originating long before ultrasound and modern lab diagnostics.
- •Due date is a midpoint, not a precise prediction. Roughly 70% of births occur between 39 and 41 weeks, while only about 5% happen on the exact estimated due date.
- •IVF pregnancies offer unusually precise dating because fertilization timing and embryo age are known directly, which has helped validate and refine due date models used in broader obstetric care.
- •A large share of modern births involve scheduling (induction or cesarean), so due date often functions as a planning anchor for prenatal care and delivery decisions rather than a literal expected birth day.