The Conception Calculator

Conceived on New Year's Eve? Here's the Due Date

Due dates & conception. Updated . Calculated with the standard pregnancy dating method used by ACOG and the NHS.

If conception happened on New Year's Eve (December 31), the baby would be due around September 23 the following year.

Conception dateDecember 31
Estimated due dateSeptember 23
Likely due window (37–42 weeks)September 2 – October 7
Last period probably startedDecember 17

Remember that sex and conception aren't always on the same day: sperm can survive for up to five days, so a holiday celebration could lead to conception a few days later.

Check your own dates with the due date calculator.

Due Date Calculator: Estimate your due date from the first day of your last period.

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This article is general information, not medical advice. Talk to a doctor or midwife about your own pregnancy or fertility.