Estimate your conception date
Choose one of the three input modes below.
Based on the average 14-day luteal phase (LMP + cycle - 14, EDD - 266, or measurement - gestational days + 14). ±5 days individual variation. Learn more
Not a medical diagnosis. Only an ultrasound can confirm your exact conception date.
How is it calculated?
Conception happens at or within 1-2 days of ovulation. For a 28-day cycle, ovulation is 14 days before the next period, so:
Formula: conception ≈ LMP + 14 days (or EDD − 266 days). For other cycle lengths: cycle length − 14 days from LMP.
Actual conception occurs within ovulation ±2 days, and because sperm survive up to 5 days in cervical mucus, the conception window spans about 6 days (Wilcox et al., NEJM 1995).
Limitations of this estimate
This is a reference estimate:
- The luteal phase averages 14 days but varies 10-16 days, giving ±2-3 day error.
- Irregular cycles make next-period prediction itself uncertain.
- IVF pregnancies should use the transfer date / embryo age — this calculator is not appropriate.
- The most accurate dating uses crown-rump length (CRL) on an 8-12 week ultrasound, which is the ACOG standard.
Typically the conception day is within ±5 days of the estimate.
Sources
Frequently asked
How do I calculate it when my cycle isn't 28 days?
The 14-day luteal phase assumption holds regardless of cycle length. So conception ≈ cycle length − 14 days from LMP. Example: a 32-day cycle puts conception at LMP + 18 days.
The more accurate methods are LH urine tests / BBT tracking, with the OB-GYN ultrasound CRL as the gold standard.
Is conception date different for IVF pregnancies?
IVF knows the exact conception (egg retrieval) and transfer dates, so general formulas are inaccurate.
Use a dedicated IVF due-date calculator that accepts embryo age (day 3/5/6) and transfer date for accurate EDD and conception timing.