Due date calculator

How the due date is estimated

Pregnancy is counted from the first day of your last menstrual period (LMP), about two weeks before conception. The estimated due date is 280 days (40 weeks) after the LMP, a method known as Naegele's rule. If your cycles are longer or shorter than 28 days, ovulation happens later or earlier, so the date shifts by the difference.

Worked example

If your last period started on January 1, 2026 and your cycle is 28 days, your due date is October 8, 2026. On April 15 you would be 14 weeks and 6 days pregnant, in the second trimester, with 176 days to go. With a 32-day cycle, the date moves to October 12.

Trimesters

• First: weeks 1 to 13
• Second: weeks 14 to 27
• Third: week 28 until birth

How accurate is it?

Very few babies arrive exactly on the due date; most are born within about two weeks of it. The American College of Obstetricians and Gynecologists recommends confirming the date with a first-trimester ultrasound, which is more accurate than counting from your period. Your doctor or midwife will set the official due date.

The page adds 280 days to the first day of your last period, then adjusts by your cycle length minus 28 days. Conception is estimated two weeks after the period start, with the same adjustment. Your current week of pregnancy counts the days from the adjusted period start to today, and the trimester dates are 14 and 28 weeks after it. Everything runs in your browser; nothing is stored or sent.