Pregnancy Due Date Calculator

How is the due date calculated?

Pregnancy lasts on average 280 days (40 weeks) counted from the first day of your last menstrual period — not from conception, which usually happens about two weeks later. The calculator uses Naegele's rule, the method doctors use: due date = first day of last period + 280 days, adjusted if your cycle is longer or shorter than 28 days.

Calculation methods

• Last menstrual period: the most common method — enter the first day of your last period and your usual cycle length.
• Conception date: if you know your ovulation or conception day, 266 days are added.
• IVF: choose a day-3 or day-5 transfer and enter the transfer date for a precise estimate.
• Known due date: if your doctor set a due date by ultrasound, enter it to see how far along you are.

The three trimesters

First trimester (weeks 1–13)

Your baby's major organs form, and symptoms such as nausea and fatigue are common. Take folic acid and avoid medicines without medical advice.

Second trimester (weeks 14–27)

Often the most comfortable stage: symptoms ease, you start to feel movement, and the anatomy scan happens around week 20.

Third trimester (weeks 28–40)

Baby grows quickly and gains weight; pregnancy is considered full term from week 37. Keep track of movements and prepare for birth.

Will my baby arrive on the due date?

Only about 4% of babies are born on their exact due date. Most births happen between weeks 38 and 42, so treat the date as a planning estimate rather than a fixed day.

⚕️ This calculator is for information only and doesn't replace prenatal care. A first-trimester ultrasound date from your doctor is the most accurate. See also the Ovulation Calculator.

Frequently Asked Questions

Last updated: 2026-10-20