Due Date from Ovulation Calculator

Add 266 days (38 weeks) to your ovulation date. For example, ovulation on April 15, 2026 gives a due date of January 6, 2027. This is more accurate than LMP-based dating when you know the actual ovulation date.

Pregnancy is 280 days from your last menstrual period (LMP) but only 266 days from conception. The 14-day difference is the time between LMP and ovulation in a typical 28-day cycle. Since this calculator starts from ovulation (which is conception day plus or minus 24 hours), you use 266.

Yes. Switch the direction to "Due Date to Ovulation Date" and enter your due date. The calculator subtracts 266 days to find the conception date and 280 days to find the equivalent LMP. This is useful when reconstructing pregnancy timing from a known delivery estimate.

The most reliable methods are: ovulation predictor kits showing a positive LH surge (ovulation occurs 24 to 36 hours later), basal body temperature charting showing a sustained 0.5 degree Fahrenheit rise, or IVF transfer day plus the embryo age. Calendar estimates alone are not exact. Always consult your healthcare provider for confirmed pregnancy dating.

Yes, when you actually know the ovulation date. LMP-based dating assumes day 14 ovulation on a 28-day cycle. If you ovulated on day 10 or day 20, the LMP method is off by up to a week. Ovulation-based dating is biologically accurate. First-trimester ultrasound dating is the gold standard and may be used to refine the estimate.

If your cycle is longer than 28 days, ovulation occurs later than day 14, so the standard LMP-based due date will be too early. Using ovulation date directly avoids this error. For a 35-day cycle, ovulation typically falls around day 21 instead of day 14, shifting the due date one week later than LMP would predict. This calculator is for planning purposes and is not medical advice.

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