Pregnancy Due Date Calculator
Free pregnancy due date calculator. Enter your last menstrual period to get your due date, current week, trimester, and week-by-week milestones.
FAQ
Frequently asked questions about pregnancy calculator.
How is the due date calculated?
Most due dates are estimated by adding 280 days, or 40 weeks, to the first day of the last menstrual period. This is called Naegele's rule and is the common starting point used in pregnancy dating.
Is the due date exact?
No. It is an estimate, not a guaranteed delivery day. Only a small percentage of babies are born on the exact due date, and normal delivery can happen across a broader window around that estimate.
Why can ultrasound dating differ from LMP dating?
Early ultrasound measures fetal size to estimate gestational age, which can be more accurate when cycles are irregular or the last period date is uncertain. Clinicians may adjust the due date if ultrasound findings differ significantly.
What trimester am I in?
Pregnancy is usually divided into three trimesters. The first runs through week 13, the second covers weeks 14 to 27, and the third starts at week 28 and continues until delivery.
Should I use this instead of medical prenatal care?
No. This tool is helpful for planning and orientation, but prenatal care, ultrasound dating, and advice from your obstetric clinician are what matter for actual medical decisions and pregnancy monitoring.