How Is Delivery Date Calculated? Pregnancy Due Date Calculator

Medically Reviewed on 5/19/2022
How Is Delivery Date Calculated
Learn how to estimate your pregnancy due date with these simple calculation methods

A healthy pregnancy should last for 280 days or 40 weeks. You can calculate your delivery date using either the date of your last menstrual period (LMP) or the date of conception.

How to calculate your delivery date using the date of your LMP

An estimated due date using the date of your LMP can be calculated with the following steps:

  1. Estimate the first day of your LMP.
  2. Count back 3 calendar months back from the LMP.
  3. Add one year and 7 days to that date.

For example, let’s say your LMP was June 27, 2018. Counting back 3 months would be March 27, 2018. After adding one year and 7 days, your delivery date would be April 3, 2019.

This 3-step due date calculation is based on a menstrual cycle that lasts for 28 days. Longer or shorter menstrual cycles may need some adjustments in the calculation.

Calculating your delivery date using LMP is fairly easy because many women can recollect the date of their last period. However, this method may not be always accurate, especially for women who:

Another method to calculate the delivery date is to use a pregnancy due date calculator:

  • Select the date of the first day of your LMP.
  • Select your average menstrual cycle length.
  • Your due date, the gestational age of your baby, and a trimester timeline will appear in the window next to the calculator.

How to calculate your delivery date using the date of conception

Another way you can calculate your due date is using your date of conception. To do this, you simply count 38 weeks ahead of the conception date to get your exact delivery date.

To figure out your conception date, however, you will need to know when you ovulated. Usually, women ovulate between 12-14 days of the menstrual cycle. Other ways to identify when you are ovulating include:

  • Noting your basal body temperature around the time of ovulation
  • Monitoring yourself for symptoms such as ovulation pain and cervical mucus
  • Using an ovulation predictor kit

How do I calculate my delivery date if I had IVF?

If you underwent in vitro fertilization (IVF) to get pregnant, the transfer date of the embryos can help you calculate your delivery date:

  • If the provider transferred the embryos 5 days after recovering the eggs, count 261 days ahead of the transfer date.
  • If the provider transferred the embryos 3 days after retrieving the eggs, count 263 days ahead of the transfer date.

Your provider will usually share all vital information on the day of embryo transfer.

What are the benefits of calculating your delivery date?

Some of the benefits of calculating your pregnancy due date include the following:

  • Helps you prepare for childbirth and delivery mentally and physically
  • Allows you to obtain proper prenatal care, which includes taking prenatal vitamins and getting prenatal screenings
  • Allows your doctor to measure the baby’s size and position throughout your pregnancy to ensure healthy growth


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Medically Reviewed on 5/19/2022
Image Source: iStock Image

Cleveland Clinic. Due Date Calculator.

University of Rochester Medical Center. Calculating a Due Date.