DueDate

Pregnancy Due Date Calculator

From the first day of your last period — your estimated due date, current week, and trimester.

First day of your last period (LMP)

Estimated due date

—

Current gestational age: —
Trimester: —

Due date from the last menstrual period

Naegele's rule adds 280 days, or 40 weeks, to the first day of the last menstrual period.

First day of last period	Estimated due date
1 January 2026	8 October 2026
15 February 2026	22 November 2026
10 March 2026	15 December 2026
1 June 2026	8 March 2027
1 September 2026	8 June 2027
20 November 2026	27 August 2027

Dating from a last menstrual period assumes a regular 28-day cycle and ovulation on day 14. An early ultrasound is more accurate, and your midwife or doctor's date is the one to plan around. Only about 4% of babies arrive on the estimated date itself.

Just an estimate

Due dates use Naegele's rule (LMP + 280 days). Only about 4% of babies arrive exactly on the due date — most arrive within two weeks either side.

Trimesters explained

First trimester (weeks 1–12): major organ formation, highest miscarriage risk, morning sickness common. Second trimester (weeks 13–27): baby grows rapidly, energy returns, anatomy scan at 18–22 weeks. Third trimester (weeks 28–40): baby gains weight, organs mature, prepare for delivery.

Frequently asked questions

How is a due date calculated?

Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If your LMP was January 1, your due date is October 8. This assumes a 28-day cycle with ovulation on day 14. For longer or shorter cycles, the calculator adjusts accordingly.

How accurate is the due date?

Only about 4% of babies are born on their exact due date. About 80% arrive within 2 weeks (38–42 weeks). First-time mothers tend to deliver a few days late on average. An early ultrasound (before 12 weeks) can refine the estimate to within ±5 days.

What if my cycle is longer or shorter than 28 days?

If your cycle is longer, ovulation likely occurred later, pushing the due date forward. For a 35-day cycle, add 7 days to the standard due date. For a 25-day cycle, subtract 3 days. Alternatively, if you know your ovulation date, add 266 days to that for a more accurate estimate.