CalcPenguin

Pregnancy Due Date Calculator

Find your estimated due date from the first day of your last period, and see how many weeks pregnant you are and which trimester you're in.

Your numbers are saved in this browser.
days

Estimated due date

8 March 2027 Monday

Weeks pregnant today
20 weeks, 6 days
Trimester
2
Days to go
134

Your estimated due date is Monday, 8 March 2027. Today you are 20 weeks and 6 days pregnant, in the second trimester.

How it's worked out

  1. Start from the first day of your last period1 June 2026
  2. Add 40 weeks (280 days)for a 28-day cycle8 March 2027
  3. Likely conceptionabout 2 weeks after the period starts15 June 2026
  4. How far along today146 days ÷ 720 weeks 6 days
  • Only about 1 in 25 babies arrive on the due date; most come within 2 weeks either side. Your doctor's or midwife's scan date takes priority.

How the due date is worked out

Due date = first day of last period + 280 days + (cycle length − 28)

Worked example

With a last period starting on 1 June 2026 and a 28-day cycle, the due date is 8 March 2027. On 25 October 2026 that's 20 weeks and 6 days, in the second trimester.

Questions people ask

How is the due date calculated?

By adding 280 days (40 weeks) to the first day of your last period, the method known as Naegele's rule. For cycles longer or shorter than 28 days, the date moves by the difference.

How accurate is the due date?

It's an estimate: only about 1 in 25 babies is born on the due date itself. Most arrive within two weeks either side. An early ultrasound gives the most reliable date.

When does each trimester start?

The first trimester runs to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 until birth.

Formula and rules last checked 25 October 2026Written and tested by the CalcPenguin teamReport a problem