Calculate How Many Weeks Baby Is

Pregnancy is a fascinating journey, and tracking your baby's development week by week can be both exciting and informative. Our pregnancy week calculator helps you determine exactly how many weeks your baby has been growing, based on your last menstrual period (LMP) or ultrasound date.

How to Calculate Pregnancy Weeks

There are two primary methods to calculate pregnancy weeks:

Last Menstrual Period (LMP): The most common method, where you count weeks from the first day of your last menstrual period.
Ultrasound Date: More precise, as it uses the date of your first ultrasound to determine your due date.

Formula

Pregnancy weeks = (Current date - LMP date) / 7 days

Pregnancy weeks = (Ultrasound date + 280 days) - Current date

Example Calculation

If your LMP was on January 1, 2023, and today is April 1, 2023:

(April 1, 2023 - January 1, 2023) = 90 days

90 days / 7 = 12.86 weeks

This means your baby is approximately 13 weeks old.

Note: Pregnancy is typically considered to be 40 weeks from conception. The first day of your last menstrual period is considered week 0, and the first trimester ends at week 12.

Pregnancy Weeks Chart

Visualizing your pregnancy journey can be helpful. The chart below shows key milestones at different weeks of pregnancy.

Pregnancy Weeks Table

Here's a table summarizing key events and developments at different weeks of pregnancy:

Week	Trimester	Key Developments
1-4	First	Implantation, organ formation, rapid cell division
5-8	First	Fetal movement, heart begins to beat, limbs form
9-12	First	Fingers and toes form, face develops, quickening felt
13-16	Second	Eyes open, hair grows, rapid growth spurt
17-20	Second	Lungs develop, bones harden, fat stores
21-24	Second	Skin becomes less transparent, baby practices breathing
25-28	Third	Baby drops into pelvis, amniotic fluid increases
29-32	Third	Bones become denser, baby gains weight
33-36	Third	Lungs mature, baby prepares for birth
37-40	Third	Full-term baby, ready for delivery

FAQ

How accurate is the pregnancy week calculator?: The calculator provides an estimate based on your LMP or ultrasound date. For precise tracking, consult your healthcare provider.
When should I get my first prenatal appointment?: It's recommended to schedule your first appointment within the first 12 weeks of pregnancy.
What happens if my baby is born before 37 weeks?: Babies born before 37 weeks are considered premature. Consult your healthcare provider for guidance.
Can I use this calculator for multiple pregnancies?: This calculator is designed for single pregnancies. For multiple pregnancies, consult your healthcare provider.
How do I know if my pregnancy week count is correct?: Your healthcare provider can confirm your pregnancy week count through ultrasound.