About pregnancy conception calculator
If you know the first day of your last period, you can estimate when conception likely took place. This also works backwards from a known due date.
How it works
Ovulation and conception usually happen about two weeks after the start of the last period in a 28-day cycle. Longer or shorter cycles move that date later or earlier.
A window, not a day
Sperm can survive for several days, so conception can happen in a window of a few days. Treat the date as an estimate and confirm with your doctor's scan.
A worked example
If the last period began on 1 January 2026 and the cycle is 28 days, ovulation is expected around 15 January, and the due date is 8 October 2026. If your cycle is 35 days, ovulation is about a week later, and the dates move accordingly.
