Pregnancy Week Calculator
Find out exactly how far along you are — weeks and days, current trimester and due date — from the first day of your last period.
You are
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Trimester —
Estimated due date —
Days until due date —
Based on a 28-day cycle. An early ultrasound gives the most accurate dating — always follow your provider's dates.
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How it works
Gestational age = days since LMP; due date = LMP + 280 days (Naegele's rule)Frequently Asked Questions
How many weeks pregnant am I?
Pregnancy is counted from the first day of your last menstrual period (LMP), not conception — so at '6 weeks pregnant' the embryo is about 4 weeks old. Enter your LMP date and the calculator gives weeks + days today.
When do the trimesters change?
First trimester: weeks 1–13. Second: weeks 14–27. Third: week 28 to birth. Full term is 39–40 weeks; anything before 37 weeks is preterm.
How accurate is dating from the LMP?
Good for regular 28-day cycles; longer or irregular cycles shift it. A first-trimester ultrasound is the most accurate dating method and takes precedence when it differs by more than a few days.