Pregnancy Weeks Converter

Pregnancy is measured from the first day of the last menstrual period (LMP). Full term is typically 40 weeks (280 days).

Weeks to months (approximate):

• Weeks 1-4: Month 1
• Weeks 5-8: Month 2
• Weeks 9-13: Month 3
• Weeks 14-17: Month 4
• Weeks 18-22: Month 5
• Weeks 23-27: Month 6
• Weeks 28-31: Month 7
• Weeks 32-35: Month 8
• Weeks 36-40: Month 9

Trimesters:

• First trimester: Weeks 1-12
• Second trimester: Weeks 13-27
• Third trimester: Weeks 28-40

Due date calculation: Due date = LMP date + 280 days (Naegele’s rule). This is the same as LMP + 40 weeks.

Note: Every pregnancy is unique. These are standard medical approximations.

Pregnancy is tracked in weeks rather than months for a good reason: months are uneven (28 to 31 days), so “weeks pregnant” is far more precise for following development and timing tests. The “nine months” everyone says is really about 40 weeks, which lands closer to ten lunar months than nine calendar ones, part of why the month math never feels quite right.

One convention surprises a lot of people: the count starts from the first day of the last menstrual period (LMP), not from conception, which happens roughly two weeks later. So at “6 weeks pregnant” the embryo is closer to 4 weeks along. It’s a clinical standard that keeps dating consistent when the exact conception date is unknown. The trimester boundaries above are the common framework, but they’re approximate and differ slightly between sources. This is general information for converting between units, not medical advice; for anything about a real pregnancy, follow a doctor or midwife.