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Calculate how many weeks pregnant you are and track your baby's development
| Week | Size Comparison | Length | Weight |
|---|---|---|---|
| 4 | Poppy seed | 0.04 in | < 1 g |
| 8 | Raspberry | 0.63 in | 1 g |
| 12 | Plum | 2.1 in | 14 g |
| 16 | Avocado | 4.6 in | 100 g |
| 20 | Banana | 6.5 in | 300 g |
| 24 | Cantaloupe | 11.8 in | 600 g |
| 28 | Eggplant | 14.8 in | 1 kg |
| 32 | Jicama | 16.7 in | 1.7 kg |
| 36 | Romaine lettuce | 18.7 in | 2.6 kg |
| 40 | Small pumpkin | 20.2 in | 3.4 kg |
A pregnancy week calculator is a specialized tool that determines exactly how far along you are in your pregnancy, expressed in weeks and days. Unlike the common assumption that pregnancy lasts nine months, medical professionals count pregnancy as 40 weeks from the first day of your last menstrual period (LMP). This calculation method, known as gestational age, is the standard used worldwide for prenatal care, developmental tracking, and delivery planning.
Understanding your exact pregnancy week is crucial for monitoring your baby's development and ensuring proper prenatal care. Each week brings new developmental milestones, from the formation of vital organs in early weeks to the development of the five senses in later stages. Healthcare providers use gestational age to schedule important screenings and tests at optimal times, such as the nuchal translucency scan at 11-14 weeks or the anatomy scan at 18-22 weeks.
The pregnancy week calculator provides more than just a number—it gives you insight into your baby's current size (often compared to fruits or vegetables for easy visualization), expected developmental milestones, and which trimester you're in. This information helps you understand what changes to expect in your body, what your baby is experiencing, and what prenatal appointments or tests should be scheduled. Many expectant parents find tracking their pregnancy week by week helps them feel more connected to their baby's growth journey.
The standard method for calculating pregnancy weeks uses your last menstrual period (LMP) as the starting point. Count the number of days from the first day of your last period to today, then divide by seven to get weeks. The remainder represents additional days. For example, if 101 days have passed since your LMP, you are 14 weeks and 3 days pregnant (101 ÷ 7 = 14 remainder 3). This method assumes a regular 28-day cycle with ovulation occurring around day 14.
If you know your due date but not your LMP, you can work backward to calculate pregnancy weeks. Subtract 280 days (40 weeks) from your due date to find your reference LMP date, then calculate forward from that date to today. This reverse calculation is particularly useful if your actual LMP date is uncertain or if your due date has been adjusted based on early ultrasound measurements. Healthcare providers often refine due dates using first trimester ultrasounds, which can date pregnancies to within 3-5 days of accuracy.
Pregnancy is divided into three trimesters based on gestational age. The first trimester spans weeks 1-12, though you're not actually pregnant during the first two weeks (this is the time before conception). The second trimester covers weeks 13-26 and is often called the "honeymoon period" of pregnancy due to increased energy and decreased morning sickness. The third trimester runs from week 27 until delivery, typically around week 40, though full term is considered 37-42 weeks.
It's important to express pregnancy in weeks and days rather than months because months vary in length and don't align neatly with pregnancy progression. A pregnancy at "4 months" could mean anywhere from 13-18 weeks depending on interpretation, while "17 weeks, 4 days" is precise and universally understood by healthcare providers. This precision matters for scheduling time-sensitive tests, monitoring growth patterns, and making decisions about pregnancy management. Many pregnancy apps and calendars track your exact gestational age daily, updating automatically to show your current week and day.
Take folic acid, manage morning sickness with small frequent meals, get plenty of rest, and attend your first prenatal appointment around 8 weeks.
Enjoy increased energy, start feeling baby move around 16-20 weeks, schedule anatomy scan, and begin preparing nursery.
Attend weekly appointments in final weeks, prepare hospital bag, practice breathing techniques, and watch for signs of labor.
Use weekly guides to understand what's happening with your baby. Each week brings new developmental milestones worth celebrating.
Adjust exercise as pregnancy progresses. Walking, swimming, and prenatal yoga are great throughout all trimesters.
Track changes week by week. Contact your provider if you experience bleeding, severe pain, or decreased fetal movement.
Pregnancy dating from LMP is a standardized system that predates modern conception dating methods. Since the exact conception date is often unknown and ovulation timing varies, using the first day of the last period provides a consistent reference point. Though you're not actually pregnant during the first two weeks, this method ensures universal consistency in pregnancy tracking across all healthcare providers.
For women with regular 28-day cycles, LMP-based calculation is quite accurate, typically within 3-5 days. However, women with irregular cycles, longer or shorter cycles, or those who recently stopped birth control may find this method less precise. First trimester ultrasounds can provide more accurate dating and may adjust your estimated due date and pregnancy week calculation.
First-time mothers typically start showing between 12-16 weeks, while those who've been pregnant before may show earlier, around 8-12 weeks. Many factors affect when you show, including your body type, abdominal muscle tone, baby's position, and whether you're carrying multiples. Everyone's experience is different, and showing early or late doesn't indicate any problems.
Your healthcare provider may adjust your pregnancy week and due date based on early ultrasound measurements, typically done in the first trimester. If there's a discrepancy of more than 5-7 days between your LMP-based dating and ultrasound measurements, the ultrasound date is usually considered more accurate. After the first trimester, dating changes are rare unless there was an obvious error in initial calculations.
Each pregnancy week has characteristic developmental milestones. Use week-by-week pregnancy guides to understand what's happening with your baby's development and what physical changes you might experience. Remember that these are general guidelines—every pregnancy is unique, and slight variations in development timing are normal and expected.
Pregnancy weeks always include remaining days for precision. Calculate total days from your LMP to today, divide by 7 for weeks, and the remainder is days. For example, 95 days equals 13 weeks and 4 days (95 ÷ 7 = 13 remainder 4). You'd say you're "13 weeks, 4 days pregnant" or write it as "13+4 weeks." This precision is important for scheduling time-sensitive tests and procedures.
The first trimester ends at 12 weeks (some sources say 13 weeks), the second trimester runs from 13-26 weeks, and the third trimester begins at 27 weeks until delivery. These divisions help organize prenatal care and developmental expectations, though the transitions between trimesters are gradual rather than marked by sudden changes.
Pregnancy is actually closer to 10 months when measured accurately. The 40-week gestation period equals approximately 280 days or 9 months and 1 week. The confusion arises because months vary in length (28-31 days), while pregnancy is measured in precise weeks. Medical professionals always use weeks rather than months to avoid ambiguity in tracking pregnancy progression and fetal development.
Calculate your estimated due date
Estimate your baby's current weight
Estimate when conception occurred
Track healthy weight gain
Predict your fertile window
Calculate implantation timing
This calculator provides estimates for educational purposes only and should not replace professional medical advice. Pregnancy dating may vary based on individual factors, cycle irregularities, and ultrasound measurements. Always consult your healthcare provider for accurate pregnancy dating, personalized guidance, and to address any concerns. If you experience unusual symptoms, bleeding, severe pain, or decreased fetal movement, contact your healthcare provider immediately.