How are pregnancy weeks counted?

Pregnancy weeks are counted from the first day of your last menstrual period (LMP), not from conception. Conception typically occurs about 2 weeks after LMP.

How do I calculate my due date?

Add 280 days (40 weeks) to the first day of your last menstrual period. This is Naegele's rule. Only about 5% of babies are born on their exact due date.

When does each trimester start?

First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27–40.

What week is considered full term?

Full term is defined as 39–40 weeks. Early term is 37–38 weeks, late term is 41 weeks, and post term is 42+ weeks.

How accurate is the due date calculation?

The LMP-based due date is accurate when periods are regular (28 days). Ultrasound in the first trimester provides more accurate dating. Only about 5% of babies are born on the due date.

How are pregnancy weeks counted?

From the first day of your last menstrual period (LMP), not from conception. Conception occurs ~2 weeks after LMP.

How do I calculate my due date?

Add 280 days (40 weeks) to the first day of your LMP. This is Naegele's rule.

When does each trimester start?

1st trimester: weeks 1–12. 2nd trimester: weeks 13–26. 3rd trimester: weeks 27–40.

What week is considered full term?

Full term: 39–40 weeks. Early term: 37–38 weeks. Late term: 41 weeks. Post term: 42+ weeks.

How accurate is the due date calculation?

LMP-based date is accurate for regular 28-day cycles. First trimester ultrasound is more accurate. Only ~5% of babies are born on their due date.

Weeks Pregnant Calculator

Calculate exactly how many weeks pregnant you are. Get your due date, trimester, and upcoming milestones from your last period or conception date.

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First Day of Last Period

Your Results

Weeks Pregnant: 20 weeks 0 days

Weeks + Days	20w 0d
Trimester	2nd
Due Date	August 16, 2026
Days Until Due Date	139

Upcoming Milestones

Week 24Viability threshold — survival outside womb possible

Week 28Third trimester begins

Week 32Baby practices breathing movements

⚕️ Always confirm dates with your healthcare provider via ultrasound.

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How This Calculator Works

Due Date = LMP + 280 days (Naegele's rule)

Weeks = (Today − LMP) ÷ 7

Frequently Asked Questions

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Calculations are for educational purposes only. Consult a qualified financial advisor for personalized advice.