Conception Calculator
Find when you most likely conceived based on your last period, due date, or ultrasound — useful for planning, dating confirmation, or curiosity.
Reviewed by Pregora Editorial Team · Last updated 2026-04-26
Tip: The calculator below shows your conception date in every result, regardless of which method you use. Pick the method that matches the data you have.
Monday, December 7, 2026
224 days to go
Important: Only ~5% of babies are born on their estimated due date. Most healthy pregnancies deliver between 37 and 42 weeks.
Frequently asked questions
How is the conception date calculated?▾
For natural pregnancies: conception happens around ovulation, which is approximately 14 days after the first day of your last period (for a 28-day cycle). The formula: conception date = LMP + (cycle length − 14).
Can I tell exactly when I conceived?▾
Not exactly — conception happens at fertilisation, which is within 24 hours of ovulation. Sperm can survive 5 days, so the 'when' is technically a 5-day window. The most likely day is on or one day after ovulation.
How accurate is the conception calculator?▾
For regular 28-day cycles with known LMP, accurate within ±3 days. Irregular cycles introduce more variation. Early ultrasound is the most accurate way to confirm dating.
Why do due dates use 280 days but conception only 266?▾
Because pregnancy is counted from the first day of your last period, not from conception. Ovulation/conception happens about 14 days after LMP. So 280 (LMP-based) − 14 (LMP to conception) = 266 days from conception to delivery.
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