Pregnancy Due Date Calculator
Estimated due date from the first day of your last period (Naegele's rule).
Formula: Naegele's rule: LMP + 280 days
Worth Knowing
Naegele's rule adds 280 days to the first day of your last menstrual period, assuming a regular 28-day cycle with ovulation on day 14 — which is why the estimate shifts if your cycles are longer or shorter. Only about 4% of babies actually arrive on their due date; most births fall within a two-week window on either side. An early ultrasound dates a pregnancy more accurately than the last-period method, especially for irregular cycles, so treat this as a first estimate.
How to Use
- Enter Last menstrual period into the Pregnancy Due Date Calculator above.
- Your result appears instantly as you type — there's no submit button or page reload.
Formula
Naegele's rule: LMP + 280 days