Due Date Calculator
When is My Baby Due?
A pregnancy typically lasts about 280 days, or 40 weeks, counted from the first day of your last menstrual period. A due date calculator uses that standard to estimate your delivery date, how far along you are, and which trimester you are in.
Enter the first day of your last menstrual period, and the calculator adds 280 days to find the due date. It also shows your current week and day of pregnancy, the trimester, and how many weeks remain. Your healthcare provider may fine-tune the date with an early ultrasound.
Frequently Asked Questions
How is a due date calculated?
The most common method is Naegele’s rule: take the first day of your last menstrual period, add 280 days (40 weeks). Because ovulation and cycle length vary, only about 4% of babies arrive exactly on their due date - most come within two weeks either side.
Why is pregnancy counted from my last period?
Because the exact day of conception is usually unknown, while the first day of the last period is easy to recall. The 40-week count starts two weeks before conception, which is why you are considered 2 weeks pregnant at the moment of fertilization.
Can the due date change?
Yes. An early ultrasound (typically 8-13 weeks) measures the baby and can adjust the due date by days or weeks if the size differs significantly from what the menstrual calculation predicts. After the first trimester, dates usually stabilize.