Pregnancy Due Date
Calculator
Find out when your baby is likely to arrive, which week you're in right now, and your baby's size this week — from your last period or conception date.
First day of last period
Average cycle length
Free, instant — no sign-up needed for the result.
How it works
Doctors count pregnancy from the first day of your last menstrual period (LMP) — not from conception. A full-term pregnancy is about 280 days (40 weeks) from the LMP. This calculator applies Naegele's rule and adjusts for your cycle length, since ovulation happens later in longer cycles.
If you know your exact conception or ovulation date (for example, with IUI), the calculator adds 266 days to that instead — the same estimate from the other direction.
Frequently asked questions
How is the due date calculated?
We use Naegele's rule — 280 days (40 weeks) from the first day of your last menstrual period, adjusted for your average cycle length. If you enter a conception date instead, we add 266 days.
How accurate is a due date calculator?
It's an estimate. Only about 5% of babies arrive exactly on their due date — most are born within two weeks either side. Your doctor may refine the date after your first ultrasound.
What if my cycles are irregular?
With irregular cycles the LMP method is less reliable. An early dating ultrasound gives the most accurate due date — mention your cycle pattern to your doctor.
What week of pregnancy am I in?
The calculator shows your current week and trimester based on today's date, along with your baby's approximate size and key developments this week.
This calculator gives an estimate for awareness only and is not a medical diagnosis. Your doctor will confirm your due date, usually with an early ultrasound.