How To Calculate Your Due Date

Are you concerned you might be pregnant? If you’re experiencing pregnancy symptoms maybe one of the first things you want to know is to calculate your due date, but finding out if you’re pregnant at all would probably be first. Even if you are just generally curious about what your due date could be, it’s a good idea to know.

A person’s due date is the estimated date of when an unborn infant will arrive, and it’s important to have an idea of when that will be for planning purposes. Here’s how to calculate your due date using a pregnancy planner and other methods.

Calculate Your Due Date With a Pregnancy Planner

One of the easiest ways to calculate your due date is by using a pregnancy planner. These planners or predictors are available online or as mobile apps. They can provide you with an estimated due date based on the first day of your last menstrual period. Simply enter the date and the planner will calculate your due date for you.

Some pregnancy planners also offer additional features such as a pregnancy countdown and helpful tips for each week of your pregnancy. Here are a few popular fertility apps for you to consider:

Naegele’s Rule

Naegele’s Rule is a commonly used method for calculating due dates. It is based on the assumption that the female menstrual cycle is 28 days long and that ovulation occurs on day 14. To use this method, add 7 days to the first day of your last menstrual period, then count back 3 months. For example, if your last period started on January 1st, your due date would be October 8th (January 1st + 7 days = January 8th, then count back 3 months to October).

To understand this a little better, it may be helpful to know a little more about ovulation. Ovulation happens when a mature egg is released from one of the ovaries and made available for fertilization. While it only lasts for 12 to 24 hours, you’re most likely to get pregnant in the days before and after ovulation, a window of around six days.

You may be wondering, “Can I get pregnant after I ovulate?” The answer is yes! Sperm can live for up to 5 days inside your body, so if you have sex up to 5 days before your egg is released, you can get pregnant.


An ultrasound is another way to determine your due date. This may be done during your first prenatal appointment. What is a fetus? A fetus is an unborn offspring, from the embryo stage (the end of the 8th week after conception, when the major structures have formed) until birth.

Please note, however, that ultrasounds can be off by a few days, so it’s best to use this method in combination with others.

If you think you may be between your 7th or 8th week of conception, please consider scheduling an ultrasound with us.

Calculate Your Due Date By Counting 40 Weeks

The average pregnancy lasts 40 weeks from the first day of your last menstrual period. This method involves counting 40 weeks from the first day of your last period to determine your due date. For example, if your last period started on January 1st, your due date would be October 8th (January 1st + 40 weeks = October 8th).

If you are exploring this method, it may be interesting for you to know what is happening at each stage of fetal development. This development is also known as gestational age, or pregnancy week by week. Learn more about 1st trimester (weeks 1-12), 2nd trimester (weeks 13-27), and 3rd trimester (weeks 28- 40) development stages from Mayo Clinic.

Due Date Calculator

If you’re not sure which method to use or want a more accurate calculation, you can use a due date calculator. These are available online and take into account factors such as the length of your menstrual cycle and the date of conception (if known). Simply enter the required information and the calculator will provide you with an estimated due date.

Here are a few popular due date calculator apps for your consideration:

Other Things to Consider

Keep in mind that your due date is just an estimate and your arrival time could be earlier or later than expected. Only about 5% of babies are born on their due date. Additionally, if you have irregular periods or are unsure of the date of your last period, your due date may be more difficult to determine. In these cases, your healthcare provider may use other methods such as an ultrasound to estimate your due date.

By using a pregnancy planner, Naegele’s Rule, ultrasound, counting 40 weeks, or a due date calculator, you can determine an estimated due date for your pregnancy. Remember to keep in mind that this is just an estimate and the actual arrival time can vary within a few weeks of your due date.

You and your health matter. If you think you may be experiencing a crisis, it is important to seek medical attention immediately.