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ARVENRA
Pregnancy & reproductive health

Conception Calculator

Estimated conception, worked back from a due date.

If you know the estimated due date, this tool works the likely conception window backwards.

Your details

From the first day of one period to the first day of the next. Default 28 days.

Typical range: 20 – 45

The values you enter are calculated in your browser only — nothing is stored or transmitted.

Fill in your details and press calculate — your result will appear here.

Formula and method

The due date minus 266 days — 38 weeks from conception — plus the six-day window around it.

Formula used

Conception = due date - 266 days; six-day window

Assumptions and limits

  • This reverse calculation is an estimate and is not suitable for establishing a conception date definitively.

Scientific sources

  1. American College of Obstetricians and Gynecologists. “Committee Opinion No. 700: Methods for Estimating the Due Date.” Obstet Gynecol. 2017;129(5):e150-e154.

    View source

  2. Wilcox AJ, Weinberg CR, Baird DD. “Timing of sexual intercourse in relation to ovulation.” N Engl J Med. 1995;333(23):1517-1521.

    View source

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