Due Date Calculator Wheel

Calculate your estimated due date, track pregnancy milestones, and see key dates throughout your pregnancy journey. This calculator helps you plan and prepare for your baby's arrival.

First Day of Last Menstrual Period Enter the first day of your last menstrual period. This is typically 2 weeks before conception.

Average Menstrual Cycle Length (days) Enter the average length of your menstrual cycle in days. The default is 28 days.

Calculation Method

Alternative Date (if applicable) For ultrasound, IVF, or conception date calculations, enter the relevant date here.

I have irregular periods

Quick Examples:

How to Use This Calculator

Enter the first day of your last menstrual period. This is typically the most accurate way to calculate your due date.
Enter your average menstrual cycle length. The default is 28 days, but adjust if your cycle is shorter or longer.
Select your preferred calculation method. Naegele's Rule is the standard method, but alternatives are available if you have additional information.
If using an alternative calculation method, enter the relevant date (ultrasound, IVF transfer, or conception date).
Check "I have irregular periods" if applicable, which will adjust the calculation to account for cycle variability.
Click "Calculate" to see your estimated due date and important pregnancy milestones.

Formula Used

Naegele's Rule: Due Date = LMP + 280 days (or LMP + 7 days - 3 months + 1 year)

Adjusted for Cycle Length: Due Date = LMP + (280 - (28 - Cycle Length)) days

Where:

LMP = First day of Last Menstrual Period
280 days = Average pregnancy duration (40 weeks)
28 days = Standard menstrual cycle length
Cycle Length = Your actual menstrual cycle length

For alternative methods:

Ultrasound-Based: Uses fetal measurements to estimate gestational age
IVF Transfer Date: Calculates from embryo transfer date (usually 266 days for 3-day embryo or 280 days for 5-day blastocyst)
Known Conception Date: Adds 266 days to conception date

Example Calculation

Real-World Scenario:

Let's calculate the due date for someone whose last menstrual period started on January 15, 2023, with a 30-day menstrual cycle.

Given:

Last Menstrual Period (LMP) = January 15, 2023
Average Cycle Length = 30 days
Calculation Method = Naegele's Rule

Calculation:

Standard Due Date (28-day cycle) = January 15 + 280 days = October 22, 2023

Adjustment for 30-day cycle = 280 - (28 - 30) = 282 days

Adjusted Due Date = January 15 + 282 days = October 24, 2023

Result: The estimated due date is October 24, 2023. Key milestones would include the end of the first trimester (April 15, 2023), viability point (July 15, 2023), and the start of the third trimester (August 15, 2023).

Why This Calculation Matters

Practical Applications

Scheduling prenatal care appointments and tests
Planning maternity leave and work arrangements
Preparing your home and family for the new arrival
Tracking fetal development milestones

Key Benefits

Provides a timeline for pregnancy milestones
Helps identify important prenatal screening windows
Assists in monitoring fetal growth and development
Reduces anxiety by providing clear expectations

Common Mistakes & Tips

A common mistake is using the date of conception or the end of your last period instead of the first day. The first day of your last menstrual period is the standard starting point for pregnancy calculations because it's a definite date that most women can recall, while conception date is often unknown.

Many calculators assume a 28-day cycle, but if your cycle is shorter or longer, this can significantly affect your due date. For example, with a 24-day cycle, your due date would be about 4 days earlier than the standard calculation, while with a 32-day cycle, it would be about 4 days later.

Remember that a due date is an estimate, not an exact science. Only about 5% of babies are born on their due date. Most healthcare providers consider a pregnancy "full term" between 39 and 41 weeks, and babies born between 37 and 42 weeks are considered within the normal range. Plan for your baby's arrival in the weeks surrounding your due date.

Frequently Asked Questions

Due date calculations are estimates that are typically accurate within 5 days before or after the calculated date when based on a known last menstrual period. Early ultrasounds (before 12 weeks) can improve accuracy to within 3-5 days. However, many factors can affect when a baby is actually born, and only about 5% of babies are born on their exact due date.

If you don't know the date of your last menstrual period, your healthcare provider will likely use an early ultrasound to estimate your due date. Ultrasounds in the first trimester are quite accurate for dating pregnancies, typically within 3-5 days. If you've had irregular periods or were using hormonal birth control when you conceived, an ultrasound-based due date is generally more reliable than one based on menstrual dates.

Yes, due dates can be adjusted during pregnancy, especially if there's a significant discrepancy between menstrual dating and ultrasound measurements. In early pregnancy, if an ultrasound differs from the menstrual-based due date by more than 5-7 days, your healthcare provider may adjust your due date. Later in pregnancy, ultrasound measurements become less accurate for dating, so adjustments are less common after the first trimester.

References & Disclaimer

Medical Disclaimer

This due date calculator provides estimates based on standard pregnancy dating formulas. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding your pregnancy or medical condition.

References

American College of Obstetricians and Gynecologists: How Your Fetus Grows During Pregnancy - Official information on fetal development and pregnancy dating.
National Institute of Child Health and Human Development: Due Date Calculator - Information about pregnancy dating and due date calculation methods.
American Society for Reproductive Medicine: Facts About Figuring Out Your Due Date - Detailed explanation of different methods for calculating due dates.

Accuracy Notice

This calculator provides estimates based on standard formulas and averages. Individual pregnancies may vary, and factors such as irregular cycles, multiple pregnancies, or medical conditions can affect accuracy. The calculator is most accurate for women with regular menstrual cycles and singleton pregnancies. Always consult with your healthcare provider for personalized information about your pregnancy.

About the Author

Kumaravel Madhavan

Web developer and data researcher creating accurate, easy-to-use calculators across health, finance, education, and construction and more. Works with subject-matter experts to ensure formulas meet trusted standards like WHO, NIH, and ISO.

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