Conception Calculator
Work backwards from a due date, or forwards from the first day of your last period, to estimate the conception date and the fertile window around it — a quick planning reference for couples tracking pregnancy timing.
Enter your details above and the result will appear here.
How to use
- Choose whether to start from your due date or your last period.
- Enter the date (and cycle length if using LMP).
- The estimated conception date and fertile window appear instantly.
Note
From a due date, conception is estimated as due date minus 266 days (38 weeks). From LMP, ovulation is estimated as LMP plus cycle length minus 14 days. The fertile window is roughly the 5 days before ovulation through the day after. Real cycles vary, so treat these as estimates. Estimate only — not medical advice.