Home Pregnancy Countdown Calculator Pregnancy Countdown Calculator When was the first day of your last menstrual period? Conception Occurred: First Trimester Ends (12 weeks): Second Trimester Ends (27 weeks): Estimated Due Date (40 weeks): On you will be weeks pregnant. About the pregnancy calculator These dates should be used as an estimates only. They are not an exact calculation. The calculator may not provide an accurate reading if you have irregular ovulation or menstrual periods. Always consult your physician or doctor to determine your correct due date.