The Reverse Due Date Calculator on this page will answer the following questions based on a due date or a birthdate:
This free online conception calculator will determine the conception date -- including the day of the week -- based on the selected month, day, and year of your pregnancy due date.
Plus, unlike other conception calculators, this calculator includes selectable dates dating back 100 years, which means it can also be used to calculate conception dates and days of the week for any dates of birth occurring within the past 99 years.
Want to know what date and day of the week you were likely conceived on? Simply select your birthday (or due date if you were born premature or late) and click the "Calculate" button.
Note that if you want to calculate what date your baby is due to be born on, please visit the Pregnancy Due Date Predictor -- which also includes How to Calculate Due Date based on Naegele's Rule.
Or, if you'd like to track your (or a loved one's) pregnancy term, be sure to visit the Pregnancy Countdown Calculator, which tells you the days, weeks, and months along and remaining. It also includes a countdown meter and printable calendar.
With that I invite you to use the reverse due date calculator to estimate the date and day of the week your baby was conceived on (or any one else for that matter).
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Pregnancy due date (or birthday): Select the month, day, and year your baby is due. Note that you can also select any birthday to calculate when you or someone else was most likely conceived.
Estimated date of conception: This is 266 days (38 weeks) subtracted from the selected pregnancy due date (the average human gestation period per Naegele's Rule).
Last period date: This is 14 days prior to conception (assuming ovulation occurred on day 14 of your menstrual cycle).