Estimated due date
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How far along
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Trimester
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Find your estimated due date, how far along you are, and your trimester.
A pregnancy due date is usually worked out with Naegele's rule: take the first day of your last menstrual period (LMP), and add 280 days (40 weeks). This assumes a regular 28-day cycle with ovulation around day 14. The calculator above does this for you and also shows how far along you are and which trimester you are in.
Why it is an estimate. Only about 1 in 20 babies actually arrive on their exact due date. A normal, full-term birth can happen any time from 37 to 42 weeks. If your cycle is longer or shorter than 28 days, or irregular, the LMP-based date can be off by several days, which is why an early ultrasound (the "dating scan") is often used to confirm or adjust it.
The trimesters. The first trimester runs to about week 13, the second from 14 to 27, and the third from 28 to birth. Knowing your week helps you follow typical development milestones and time appointments and scans. Treat the due date as the middle of a likely window, not a fixed appointment.