How to Calculate Your Pregnancy Due Date

Knowing how to determine due date can help you get a sense of your pregnancy timeline, schedule prenatal visits, and prepare for the arrival of your baby. Your estimated due date is an idea of when your baby may be born, but it’s not an exact prediction.

Healthcare professionals use information such as the date of your last period, the date of conception and ultrasound results to estimate when your pregnancy will reach 40 weeks.

1. Calculate Your Due Date By Your Last Menstrual Cycle

One of the most common ways to estimate your due date is from the first day of your last menstrual period (LMP).

From this date a normal pregnancy lasts about 280 days or 40 weeks

How to calculate your estimated due date:

Find out the first day of your last period.
Add 280 days or 40 weeks.
This is your estimated due date.

For example, if your last menstrual period began on January 1, your estimated due date will be about October 8 (in a non-leap year).

That method assumes a 28-day menstrual cycle. If your cycle is longer or irregular, or shorter, you may need to adjust this estimate.

2. Calculate Your Due Date from Conception

If you know when conception happened, you can estimate your due date by adding 266 days (38 weeks) to that date.

For instance, if you got pregnant on January 15th, your due date would be approximately October 8th.

But it can be hard to pin down when conception occurred, because ovulation can happen at different times, and sex can happen days before fertilisation.

3. Ultrasound scan Use

An ultrasound scan can help you find out how far along in your pregnancy you are. An early pregnancy ultrasound measures the developing embryo and can give a more precise estimate if you do not know when your last menstrual period was or if your menstrual cycles are irregular.

Your health professional may use the scan results along with your menstrual history to determine or confirm your estimated delivery date.

4. Test a Pregnancy Due Date Calculator

A pregnancy due date calculator makes it easy. Depending on the tool, you may be asked to give the date of your last menstrual period, the average length of your menstrual cycle, or the date of conception.

The calculator will then give you an estimated due date, and it can also tell you your current week of pregnancy.

Remember, this is an estimate, not a promise of an exact delivery date.

5. Know Your Weeks of Pregnancy

Pregnancy is usually divided into three trimesters:

First trimester: Weeks 1 to 13
Second trimester: 14-27 weeks
Third trimester: Week 28 through birth

Pregnancy dating is based on the first day of your last menstrual period Conception has usually not yet taken place in the first two weeks of pregnancy dating.

If You Have Irregular Periods?

If your periods are irregular, or you don’t know when your last period was, it can be more difficult to work out your due date. An early ultrasound and guidance from a qualified health care professional can provide a more reliable estimate.

Can Your Baby Come Early or Late?

Yes. Your estimated due date is around 40 weeks pregnant, but babies can arrive early or late. Only a small number are born on the exact predicted date.

Your health care professional will follow your pregnancy and tell you what to expect as you get closer to your due date.

Conclusion

Knowing how to calculate due date will let you track your pregnancy and get ready for childbirth. You might be able to estimate your due date based on your last menstrual period or conception date, or have it measured by ultrasound.

If you are unsure of your dates, go to your prenatal visits and talk to your health care provider to get the most accurate dating of your pregnancy.