With this module you can compute dates during and after your pregnancy.
If you enter a negative value for "Days before birth", "Weeks before birth", or "Months before birth" then the result that will be printed after it will indicate the days, weeks, or months after the birth date.
With this numerical module you can not compute the conception date from the birth date. It is more accurate to compute the conception date from the date of the beginning of the last menstruation. If you still want to have an indication of the conception date given the birth date then go to the conception date calculator.