Due Date Calculator

- May 09, 2025
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Calculate your estimated due date based on your last menstrual period, conception date, or ultrasound information. This calculator provides an approximate due date and important pregnancy milestones.

Calculation Method

Advanced Options

About Due Date Calculations

The average pregnancy lasts about 40 weeks (280 days) from the first day of the last menstrual period (LMP). Due dates are just estimates – only about 5% of babies are born on their exact due date.

Calculation Methods
  • Last Menstrual Period (LMP): The most common method. Adds 280 days (40 weeks) to the first day of your last period.
  • Conception Date: Adds 266 days (38 weeks) to the date of conception, which is typically about 14 days after the start of the last period.
  • Ultrasound Dating: Uses measurements taken during an ultrasound to determine gestational age, then calculates the due date.
Trimesters

Pregnancy is divided into three trimesters, each lasting about 13-14 weeks:

  • First Trimester: Weeks 1-13 (development of major organs and systems)
  • Second Trimester: Weeks 14-26 (rapid growth and movement)
  • Third Trimester: Weeks 27-40 (final development and preparation for birth)
Terms to Know
  • Gestational Age: Time measured from the first day of the last menstrual period (LMP)
  • Embryonic Age/Fetal Age: Time measured from conception (typically 2 weeks less than gestational age)
  • Full-term: Between 39 weeks, 0 days and 40 weeks, 6 days
  • Early-term: Between 37 weeks, 0 days and 38 weeks, 6 days
  • Late-term: Between 41 weeks, 0 days and 41 weeks, 6 days
  • Post-term: 42 weeks, 0 days and beyond

Understanding the Due Date Calculator

The Due Date Calculator is a useful tool for anyone expecting a baby. It estimates when your baby is likely to arrive based on specific dates related to your Pregnancy. You can input your last menstrual period, conception date, or ultrasound information. This simple tool helps you get a good idea of your due date and key pregnancy milestones along the way.

Selecting a Calculation Method

To use the calculator effectively, you can choose from three different methods. Each method uses different starting points to estimate your due date. Here’s a brief overview:

  • Last Menstrual Period (LMP): This is the most common method, adding 280 days to the first day of your last period.
  • Conception Date: This method adds 266 days from the conception date, which is usually about two weeks after your last period began.
  • Ultrasound Data: This method relies on ultrasound measurements to determine gestational age and calculate your due date.

Inputting Your Information

Once you select a calculation method, you will need to provide the relevant dates. For LMP, you enter the first day of your last period and the average length of your menstrual cycle. If you choose conception, you just enter the conception date. Lastly, if ultrasound data is preferred, you will need the ultrasound date and gestational age at that time.

Key Pregnancy Milestones

Besides calculating your due date, the calculator also outlines important pregnancy milestones. These milestones can help you track your pregnancy's progress. They include when your first and second trimesters will end, as well as your current gestational age. This information can be very useful for expecting parents.

Advanced Options for Personalisation

The calculator also includes advanced options that can enhance your experience. You have the choice to show a pregnancy calendar, which visualises your pregnancy journey week by week. Additionally, there’s an option to display lunar months if you follow that system. These features allow for a more tailored approach to tracking your pregnancy.

Interpreting Your Results

After inputting your details, the calculator will provide you with several results. You’ll get your estimated due date, your current gestational age, and when your trimesters will end. Additionally, you will receive a table of significant milestones throughout your pregnancy. These results give you a clearer understanding of your pregnancy timeline.

The Science Behind Due Dates

Understanding due dates can help you prepare for your baby's arrival. The average pregnancy lasts around 40 weeks from the first day of your last period. However, it’s essential to remember that only a small percentage of babies are born on their exact due date. Knowing the different calculation methods will help you grasp how these dates are derived.

Helpful Terms for Expecting Parents

Familiarising yourself with some key terms can improve your understanding of th e pregnancy process. Here are a few important definitions:

  • Gestational Age: Time measured from the first day of your last menstrual period.
  • Full-term: A pregnancy duration considered healthy, typically between 39 weeks and 40 weeks plus 6 days.
  • Post-term: Refers to pregnancies that go beyond 42 weeks.