How accurate is this?

It's a well-established estimate but only ~4% of babies are born on their calculated due date. Most arrive within two weeks either side. An early ultrasound gives a more accurate date.

My cycle isn't 28 days — does this still work?

Yes — enter your average cycle length and we shift the due date accordingly. If your cycles are very irregular, ask your provider for a dating scan.

Can I use a conception date instead?

For this tool, no — enter the first day of your last period. If you only know the conception date, subtract 14 days and use that as the LMP.

Pregnancy Due Date Calculator

Estimated due date, current week and trimester, based on your last menstrual period and cycle length.

Your details

First day of last period

Average cycle length

days

Estimated due date

Saturday, 6 March 2027

You are currently

8w 4d

Trimester 1

Days until due

219

Pregnancy timeline (0 – 40 weeks)

1st trimester2nd trimester3rd trimester

Not medical advice. This is an estimate based on a standard 40-week pregnancy. Only around 4% of babies arrive on their exact due date. Your midwife or doctor will confirm gestational age via ultrasound.

How this is calculated

The most common estimate uses Naegele's rule: due date = first day of last menstrual period (LMP) + 280 days (40 weeks). Because ovulation happens roughly two weeks into a 28-day cycle, longer cycles push the due date later. We adjust by (cycle length − 28) days.

Gestational age is measured from the LMP, so at conception you're already considered ~2 weeks pregnant. Trimesters are commonly split as: 1st (weeks 0–12), 2nd (13–26), 3rd (27–40).