How To Calculate How Many Weeks Pregnant You Are

Calculating your pregnancy weeks is crucial for tracking your baby’s growth and development. Here’s how to do it accurately.

1. Enter your last menstrual period (LMP) date.
2. Optionally, enter your conception date if known.
3. Click ‘Calculate’.

Our calculator uses Naegele’s rule, which adds 280 days (40 weeks) to your LMP to estimate your due date. If you enter a conception date, we’ll use that instead.

Pregnancy Weeks vs. Fetal Development

Average Pregnancy Length by Country

• Use Naegele’s rule for an accurate due date estimate.
• Regular prenatal check-ups help monitor your baby’s growth.
• Consider using a fertility tracker for more precise conception dating.

What if my cycle is irregular?

Use an ovulation predictor kit or track your basal body temperature for a more accurate conception date.

Can I calculate weeks based on my conception date?

Yes, our calculator allows for that. Just enter your conception date in addition to your LMP.

World Health Organization – Pregnancy

Mayo Clinic – Pregnancy: Due date calculator