Due date calculator: which week of pregnancy are you in?
With this pregnancy calculator, you can see when your baby is likely to arrive and which week of pregnancy you're in right now. Just enter the first day of your last period. You can also calculate from the day of conception or enter a due date you already know.
Your estimated due date
- Week of pregnancy
- Trimester
- Until your due date
The calculated date is a guideline. Your OB-GYN or midwife will pin it down more precisely by ultrasound.
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How your due date is calculated
OB-GYNs and midwives use Naegele's rule. You count from the first day of your last period, and from there a pregnancy lasts 280 days on average, or 40 weeks. If your cycle is shorter or longer than 28 days, the due date shifts by exactly that difference.
If you know the day of conception, you add 266 days to it. Because that day often isn't known, calculating from the last period has become the standard.
What does 24+3 weeks mean?
The first number counts the completed weeks since the first day of your last period, the second the days after that. So 24+3 means 24 full weeks and 3 days. That puts you in the 25th week of pregnancy.
The three trimesters
The 1st trimester runs until the end of week 12 of pregnancy, the 2nd trimester until the end of week 27. From week 28, you're in the 3rd trimester until the birth.
Common questions about your due date
How accurate is the calculated due date?
It's a guideline. Most babies arrive in the weeks before or after it rather than on the day itself. At the ultrasound in early pregnancy, your OB-GYN may still adjust the date.
How long does a pregnancy last?
40 weeks or 280 days on average, counted from the first day of your last period. From fertilization, it's about 38 weeks.
What week of pregnancy am I in?
Enter the first day of your last period in the calculator above. You'll then see your week in the usual notation, for example 24+3.
When does the first week of pregnancy start?
From the first day of your last period, so even before fertilization. That's why, by this calculation, you're already in about week 3 when fertilization happens.
What if my cycle is irregular?
Then calculating from your last period is less accurate. In that case, the date from the ultrasound is more reliable.
