Due date calculator: when is my baby due?
Work out your due date and how many weeks pregnant you are from your last period, the day you conceived, your IVF transfer or a due date you already have, plus the key dates of your pregnancy.
When is your baby due, and how far along are you right now? Fill in what you know: the first day of your last period, the day you conceived, your IVF transfer date or a due date you already have. You'll see your due date, how many weeks and days pregnant you are, and the key dates ahead.
Nothing you enter is sent to us. It's all worked out in your own browser.
How is your due date worked out?
Pregnancy is counted from the first day of your last period, not from the day you conceived. Your due date is 280 days (40 weeks) after that day. That means for the first two weeks or so you're not actually pregnant yet: you usually conceive around ovulation, about two weeks into a 28-day cycle. Hardly anyone knows that exact day, so the period is the starting point everyone uses.
If your cycle is longer or shorter than 28 days, you probably ovulate later or earlier. The calculator moves your due date to match: with a 32-day cycle, your date comes 4 days later.
How accurate is a due date?
Not very, and that's normal. Only about 1 in 20 babies is born on their due date. Most arrive somewhere between 37 and 42 weeks.
An ultrasound in the first trimester (up to about 14 weeks) dates a pregnancy most accurately. If the scan doesn't match your period date, your doctor or midwife may change your due date to the scan date.
Due date after IVF
After IVF you know exactly how old the embryo was, so the date is more precise. With a 5-day embryo (blastocyst), your due date is 261 days after the transfer. With a 3-day embryo, it's 263 days after.
What do the weeks mean?
| Weeks | What it's called |
|---|---|
| Up to 13 weeks and 6 days | First trimester |
| 14 to 27 weeks | Second trimester |
| 28 weeks until birth | Third trimester |
| 37 and 38 weeks | Early term |
| 39 and 40 weeks | Full term |
| 41 weeks | Late term: your provider will usually bring up inducing labor |
Waiting it out past your date? Here's what 41 weeks with no signs of labor means.
FAQ
How many weeks pregnant am I?
Count the weeks from the first day of your last period. On the day your period is due (in a 28-day cycle), you're already 4 weeks pregnant, even though you conceived only about two weeks before.
Can my due date change?
Yes. Your doctor or midwife may move it after your first-trimester ultrasound if the baby's measurements don't fit your period date. After that, it usually stays the same.
I don't know when my last period was. What now?
Then an ultrasound gives the best estimate. Book your first prenatal appointment and mention that you're not sure of the date.
What if I conceived on a known day?
Choose "the day I conceived" in the calculator. Your due date is then 266 days (38 weeks) after that day.
Going through this right now? Talk to other parents in our 1st trimester forum.
Sources
- ACOG: Committee Opinion 700, Methods for estimating the due date
- ACOG: Committee Opinion 579, Definition of term pregnancy
- ACOG: How your fetus grows during pregnancy (FAQ)
- NHS: Pregnancy due date calculator
- Khambalia AZ et al.: Predicting date of birth and examining the best time to date a pregnancy, Int J Gynaecol Obstet 2013
