How is a due date calculated?

The standard method (Naegele's Rule) adds 280 days (40 weeks) to the first day of your last menstrual period.

How accurate is the due date?

Only about 5% of babies are born on their exact due date. Most births happen within 2 weeks before or after the estimated date.

Most home pregnancy tests are accurate from the first day of a missed period. Testing a few days earlier may give a false negative.

根据末次月经（LMP）计算预产期、当前孕周和孕期。

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