Pregnancy Conception Calculator

This pregnancy conception calculator estimates a likely conception date and a possible conception range. It works from three input methods: due date, last period start date with menstrual cycle length, or ultrasound date with pregnancy weeks and days. Results include the estimated conception date, range start, range end, due date, and range length.

How to use this calculator

Choose the method that fits your information. Use due date when you already have an estimated due date. Use last period when you know the first day of the last menstrual period and your typical cycle length. Use ultrasound when you have a scan date and the gestational age shown on the report.

For the reverse view, try the reverse due date calculator. To see pregnancy age as of today, use the gestational age calculator.

How it works

The due date method counts backward 38 weeks from the estimated due date.

$estimated\ conception = due\ date - 266\ days$

The last period method estimates ovulation as cycle length minus 14 days after the period start. The ultrasound method subtracts the scan gestational age, then adds about 14 days to move from gestational dating to estimated conception.

Worked example

If the due date is October 8, subtracting 266 days gives an estimated conception date around January 15. The calculator also shows a range from about five days before that date to one day after it.

Important context

Conception dating is approximate. Ovulation can vary, fertilization timing is not visible on a calendar, and a date range cannot prove when intercourse occurred. Use healthcare guidance for medical decisions.