Conception Date Calculator
Enter an expected or actual due date to estimate the likely conception date.
About this calculator
This conception calculator works backward from a due date using the standard 280-day pregnancy estimate, placing likely conception around 266 days (38 weeks) before delivery — roughly two weeks after the last menstrual period.
Actual conception can vary by several days depending on individual cycle length and ovulation timing, so treat the result as a helpful estimate rather than a precise figure.
How it works
Enter the due date
Use the confirmed or estimated due date from a pregnancy test or provider.
Calculate
The calculator works backward using the standard 280-day pregnancy length.
Review the estimate
See the estimated conception date and corresponding last menstrual period date.
Frequently asked questions
How precise is this estimate?
It's based on population averages and can be off by several days for individuals with longer or shorter cycles.
Can this be used for legal or paternity purposes?
No — for anything requiring precision, rely on medical dating (ultrasound) or genetic testing rather than a calendar estimate.