Pregnancy Due Date Calculator

What Does Due Date Mean in Pregnancy?

Pregnancy is an incredible journey where a woman carries one or more children for about nine months. The big moment typically happens around 40 weeks after the first day of her last menstrual period, or 38 weeks after conception. The World Health Organization states that a normal pregnancy can last anywhere between 37 and 42 weeks.

So, when you announce you're pregnant, the first question you'll often hear is, "When are you due?" The truth is, only a small percentage of babies actually arrive on their due date. That’s why it’s called the Estimated Delivery Date (EDD).

How Is the Due Date Calculated?

There are several ways to calculate a due date, but one of the most straightforward is to count 38 weeks from the day of conception—if you happen to know it. The average pregnancy lasts 38 weeks from the moment of conception.

However, it’s rare for women to know the exact date they conceived. Even if you only had sex once during your fertile window, pregnancy doesn’t happen immediately unless you were ovulating right at that moment. Sperm can survive in the fallopian tubes for up to five days, which means conception could occur days after the actual act. That's when the magic happens, and you get pregnant.

The First Day of Your Last Period

Most doctors rely on the first day of your last menstrual period (LMP) to calculate your due date. This method involves counting forward 40 weeks, or 280 days, from the LMP. You can also add seven days and then subtract three months from that date to get a rough estimate.

Keep in mind, this is just an estimated due date—your baby won’t necessarily arrive on that exact day. In fact, only around 4% of babies are born on their predicted due date.

Determining the Date of Conception

If you want to know the exact date of conception, you might think ovulation day would give you the answer. While it's true that a human egg can only be fertilized for about 12 to 24 hours after ovulation, pinpointing the exact date is tricky. Ultrasound estimates and ovulation tracking aren’t always precise either. To complicate things further, sperm can hang around in your reproductive system for up to five days after sex, meaning conception could happen even if intercourse didn’t occur on ovulation day.

Can Your Due Date Change?

Your due date isn’t set in stone. If an early ultrasound scan in the first trimester shows your baby is growing faster or slower than expected, your doctor might adjust your due date. This is more common for women with irregular menstrual cycles, making it harder to determine the exact conception date.

During an ultrasound, your healthcare provider will measure your baby to see how far along you are and possibly adjust the due date based on that information.

Can Ultrasound Help Calculate Your Due Date?

Yes, an ultrasound can help verify the accuracy of your due date, especially if your menstrual cycle is unpredictable. Typically, your due date is calculated based on the first day of your last period. However, if your cycle is irregular, an ultrasound performed in the first trimester can give a more reliable estimate by comparing the LMP to the baby’s size during the scan.

Can You Plan Your Due Date?

Some people love to plan and organize, but when it comes to pregnancy, many factors are out of your control. You can't predict exactly when you'll conceive, even if you track your ovulation and have plenty of unprotected sex during your fertile window. Conception can be quite random.

To give you an idea, about 65% of couples under 35 conceive within six cycles of trying, while around 45% conceive within three cycles. So even though you might want to time your pregnancy for a specific month, all you can really do is try. And even if you manage to get pregnant at the ideal time, remember, the due date is just an estimate. Babies tend to arrive when they’re ready, not according to a calendar.

Since an “average” pregnancy lasts about 40 weeks, babies usually arrive anywhere between 37 and 42 weeks.

Using a Due Date Calculator

Using a due date calculator is simple. All you need to know is the first day of your last period. Plug that into the calculator, and it will give you your estimated due date. On average, pregnancy lasts between 37 and 42 weeks from the start of your last menstrual cycle.

If you’re not sure about the first day of your last period, or if your cycles are irregular, talk to your doctor or midwife to help estimate your due date more accurately.

Announcing Your Pregnancy

The first trimester can be a nerve-wracking time for many expectant mothers due to the risk of miscarriage. Studies show that between 8 and 20% of women who know they are pregnant experience a miscarriage before 20 weeks, with about 80% of these happening within the first 12 weeks.

For this reason, some women choose to wait until after their first OB appointment—around the 7-week mark—or until 12 weeks to share the news with friends and family. Every woman is different, and there’s no right or wrong time to announce your pregnancy. Just be sure to do it when you feel comfortable and ready.