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How to Calculate Pregnancy Due Dates and Gestational Age

Quick answer

To calculate a pregnancy due date manually, apply Naegele's Rule: identify the first day of your last menstrual period (LMP), add exactly 7 days to that number, subtract 3 calendar months, and advance the calendar year by one step.

Step by step

  1. Apply naegele's rule: identify the first day of your last menstrual period (lmp)
  2. Add exactly 7 days to that number
  3. Subtract 3 calendar months
  4. Advance the calendar year by one step

The Gestational Mathematics Model

Obstetric standards define the baseline gestational period as 280 days (40 completed weeks) starting from the LMP. This calculation assumes a standard 28-day ovulation cycle. If your personal ovulation cycle is longer or shorter than the 28-day midpoint standard, the targeted delivery projection requires an equivalent directional shift. Naegele's Rule Equation: Expected Due Date (EDD) = LMP + 7 Days - 3 Months + 1 Year

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