Conception Due Date Calculator
Know when you conceived? Enter your conception date to get your estimated due date and full pregnancy timeline.
If conceived through IVF, use the fertilization date (egg retrieval date + 1 day for Day 1 embryo).
How to Calculate Due Date from Conception Date
The conception due date calculator works on a simple biological principle: human pregnancy lasts approximately 266 days (38 weeks) from the date of fertilization. Add 266 days to your conception date, and you have your estimated due date. This method is often more intuitively satisfying for mothers who know the specific day they conceived.
Unlike the standard LMP (Last Menstrual Period) method, which assumes ovulation happens exactly on day 14 of your cycle, the conception method doesn’t make any assumptions about your cycle length. This makes the calculate due date from conception date approach more personalized and potentially more accurate for women with irregular cycles.
The 266-Day Formula Explained
Due Date = Conception Date + 266 days
This 266-day average is derived from studies of natural conception cycles. Fertilization typically occurs within 24 hours of ovulation. The fertilized egg then takes about 6–10 days to implant in the uterine wall, after which the pregnancy clock officially begins. The 266-day count includes all stages of fetal development from a single cell to a full-term newborn.
Tracking Your Conception Date
Most women estimate conception from ovulation tracking. Reliable methods include ovulation predictor kits (OPKs) that detect the LH surge 24–36 hours before ovulation, basal body temperature (BBT) charts (temperature rises 0.2°C after ovulation), cervical mucus monitoring (clear, stretchy “egg-white” mucus signals peak fertility), and fertility apps that combine multiple data points. IVF patients have the most precision — the exact fertilization date is documented by the embryology lab.
When Conception and LMP Dates Differ
If you have both a known LMP and a known conception date, they may give slightly different due dates. This is normal. The conception date method is generally more accurate if the date is certain. However, your OB or midwife will ultimately use a combination of your dates and your dating ultrasound (typically at 8–10 weeks) to establish your official estimated due date (EDD).
Frequently Asked Questions
Common questions answered by our medical team
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