Naegele's Rule
The standard formula adds 280 days (40 weeks) to the first day of your last menstrual period. It assumes ovulation around day 14 — close enough for a 28-day cycle.
HealthCalculator
Pregnancy Due Date Calculator
Estimate your due date and conception date from the first day of your last menstrual period, with current week and trimester.
What it means
About this calculator.
Cycle length adjustment
If your cycle is longer or shorter than 28 days, ovulation shifts by the same amount. We add (cycle length − 28) days to the due date so the estimate stays grounded in the likely conception date.
FAQ
Questions people usually have.
How accurate is this?
Only about 5% of babies arrive on the exact estimated date. Most fall in a 1-2 week window on either side. An early ultrasound is more accurate than LMP-based estimates.
Is this medical advice?
No. This is a quick estimate. For prenatal care, decisions about delivery, or anything clinical, talk to your OB or midwife.
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