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Conception Calculator

Estimate your most fertile days for the next 6 cycles and the corresponding due dates if conception occurs.

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The first day of your most recent period.
Typical range: 21–35. Default is 28.
Note: This provides an estimate of fertile days. Conception depends on many factors. Consult a healthcare provider for personalized advice.
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About Conception

Conception occurs when a sperm cell fertilizes an egg, typically within 12–24 hours after ovulation. This calculator helps identify the days each cycle when conception is most likely.

How this calculator works

Ovulation is estimated at (cycle length − 14) days after the start of your period. The fertile window spans 5 days before through 1 day after ovulation. The "best days" are the 2–3 days immediately before ovulation, when studies show the highest conception rates (~30%).

Tips for trying to conceive

Regular intercourse every 1–2 days during the fertile window gives the best chances. Tracking basal body temperature and cervical mucus can help confirm ovulation timing. Ovulation predictor kits (OPKs) detect the LH surge that precedes ovulation by 24–36 hours.

Due date estimates

If conception occurs, the estimated due date is about 266 days (38 weeks) later. This aligns with the standard 280 days from LMP, since ovulation is typically ~14 days after the start of the period.