Pregnancy Due Date Calculator
Calculate your estimated due date, current pregnancy week and trimester from the first day of your last period.
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How Is the Due Date Calculated?
The estimated due date follows Naegele's rule: 280 days (40 weeks) are added to the first day of your last menstrual period (LMP). Pregnancy weeks are counted from the same day, which is why the "first week" starts before conception. The tool shows your due date, current gestational age in weeks and days, the trimester, and how many days remain.
Only about 4–5% of babies arrive exactly on the due date; birth any time between weeks 37 and 42 is considered normal. Ultrasound measurements in early pregnancy may shift the estimate. This tool is informational and does not replace medical follow-up.
Frequently Asked Questions
How accurate is the due date?
It is an estimate: only about 4-5% of births happen on the exact date, and most occur within two weeks either side. First-trimester ultrasound gives the most reliable dating.
Why do pregnancy weeks start before conception?
By convention, gestational age counts from the first day of the last period — roughly two weeks before ovulation and conception. So at "6 weeks pregnant" the embryo is about 4 weeks old.
What are the trimesters?
The first trimester covers weeks 1-13, the second weeks 14-27, and the third week 28 to birth. The tool shows which one you are in.
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Pregnancy Due Date Calculator