Pregnancy Weeks Calculator: Baby Size & Milestones

Track your pregnancy week by week. Features a visual 'Baby Size' guide using fruit comparisons and calculates trimesters based on LMP or ultrasound.

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About

Knowing your exact gestational age is vital for monitoring fetal development and scheduling prenatal care. This tool calculates your current pregnancy week based on the Last Menstrual Period (LMP) or a confirmed Ultrasound Date. Unlike simple calendars, it contextualizes the numbers by comparing your baby's size to familiar fruits and vegetables, making the medical data more relatable.

Pregnancy is divided into three trimesters, each with critical developmental milestones. Accurate tracking helps expectant parents anticipate bodily changes, screen for anomalies at the correct times (e.g., nuchal translucency scan at 11-13 weeks), and prepare for labor. Use this calculator to stay synchronized with your baby's growth journey.

pregnancy gestational age due date maternal health

Formulas

The standard calculation for gestational age relies on the time elapsed since the first day of the Last Menstrual Period (LMP). It assumes a 28-day cycle.

Gestational Age = Current Date − LMP Date

This duration is usually expressed in completed weeks and days:

Weeks = floor(DaysDiff ÷ 7)

Reference Data

WeekBaby Size ComparisonLength (approx)Weight (approx)Key Milestone
4 WeeksPoppy Seed< 1 mm< 1 gBlastocyst implants in uterus.
8 WeeksRaspberry1.6 cm1 gHands and feet are forming.
12 WeeksLime5.4 cm14 gReflexes develop; end of 1st Trimester.
16 WeeksAvocado11.6 cm100 gGender may be visible on ultrasound.
20 WeeksBanana16.4 cm300 gAnatomy scan; baby can hear sounds.
24 WeeksEar of Corn30 cm600 gViability milestone; lungs developing.
28 WeeksEggplant37.6 cm1 kgEyelids open; 3rd Trimester begins.
32 WeeksNapa Cabbage42.4 cm1.7 kgFingernails fully formed.
36 WeeksPapaya47.4 cm2.6 kgBaby drops into pelvic cavity.
40 WeeksWatermelon51.2 cm3.5 kgFull term; ready for birth.

Frequently Asked Questions

Pregnancy weeks are calculated from the first day of your Last Menstrual Period (LMP), not the day of conception. This is because ovulation usually happens about two weeks after the LMP began, and the exact date of conception is often unknown. Therefore, you are technically considered '2 weeks pregnant' when conception actually occurs.
Early ultrasounds (first trimester) are generally more accurate for dating than the LMP, especially if you have irregular cycles. Most healthcare providers will adjust your due date if the ultrasound measurements differ from the LMP-based date by more than 5-7 days.
A pregnancy is considered 'full term' from 39 to 40 weeks. Going past 40 weeks is common, especially for first-time mothers. Pregnancies lasting longer than 42 weeks are termed 'post-term' and often require closer monitoring or induction of labor to ensure the baby's safety.
The fruit comparisons are approximations to help parents visualize size. Babies grow at different rates, and length (crown-to-rump vs. crown-to-heel) changes how size is measured throughout pregnancy. Always rely on your doctor's measurements for medical accuracy.