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Calculate gestational age from your LMP. See due date, trimester, and milestones.
Gestational age is the number of weeks and days since the first day of the last menstrual period (LMP), used as the standard method for dating pregnancy and estimating the due date.
Formula
EDD = LMP + 280 days (Naegele's rule) | Gestational Age = Today − LMPLMP = First day of the last menstrual period
EDD = Estimated due date (280 days from LMP)
280 days = 40 weeks — standard full-term pregnancy length
Worked Example
LMP: January 1, 2026
Did you know? Naegele's rule, the standard EDD calculation, was published by German obstetrician Franz Naegele in 1812. It assumes a 28-day menstrual cycle, yet only about 13% of women have exactly 28-day cycles (source: ACOG).
Sources
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