Pregnancy Due Date Calculator
Estimated due date from the first day of the last period — with trimester milestones and how far along the pregnancy is today.
How the estimate works
Naegele's rule: due date = last period + 280 days (40 weeks), adjusted by your cycle length (a 31-day cycle shifts it 3 days later, since ovulation comes later). Trimester 2 starts at week 14, trimester 3 at week 28.
Frequently asked questions
How accurate is a due date?
It's a midpoint, not a promise: only about 4–5% of babies arrive on the exact date, but ~90% arrive within two weeks either side. A first-trimester ultrasound gives the most accurate dating and may shift this estimate — trust the scan over the calendar.
What if my cycles are irregular?
Naegele's rule assumes ovulation at a predictable point, so irregular cycles make LMP dating unreliable. If you know your conception date, add 266 days to it instead; otherwise the dating ultrasound settles it.
Is this medical advice?
No — it's the same arithmetic midwives start from, but every pregnancy is dated and monitored individually. Confirm everything with your healthcare provider.
Last updated: 2026-07-13