Pregnancy Due Date & Gestational Age Calculator
Enter either your Last Menstrual Period (LMP) start date or your Estimated Conception Date to calculate your estimated due date and current gestational age.
Understanding Pregnancy Calculation
Calculating your estimated due date (EDD) and current gestational age is a key part of prenatal care. While these dates are always estimates, they provide a crucial timeline for monitoring fetal development and planning for birth.
How is Pregnancy Length Determined?
A full-term pregnancy is typically considered to last about 40 weeks (280 days) from the first day of your Last Menstrual Period (LMP), or 38 weeks (266 days) from the date of conception. The discrepancy arises because the LMP method assumes conception occurs approximately two weeks after the start of your last period, around the time of ovulation.
Naegele's Rule
The most common method for calculating a due date is Naegele's Rule. This rule states that you can estimate your due date by adding seven days to the first day of your LMP, then subtracting three months, and adding one year. For example, if your LMP was January 1, 2024:
- Add 7 days: January 8, 2024
- Subtract 3 months: October 8, 2023
- Add 1 year: October 8, 2024
This calculator uses a simpler method of adding 280 days directly to the LMP, which yields the same result.
Why Use LMP?
The LMP is often used because it's usually a more definite date than the exact moment of conception, which can be hard to pinpoint. However, this method works best for individuals with regular 28-day menstrual cycles.
When is Conception Date Used?
If your menstrual cycles are irregular, or if you know the exact date of conception (e.g., through IVF or precise tracking of ovulation), using the conception date can provide a more accurate estimate. In this case, 266 days are added to the conception date to determine the due date.
Gestational Age
Gestational age refers to how far along the pregnancy is, measured in weeks and days. It's calculated from the LMP or adjusted from the conception date to align with the LMP-based dating. This helps healthcare providers track the baby's growth and development against expected milestones.
Important Considerations
- Estimates, Not Guarantees: Only about 4% of babies are born on their exact due date. Most are born within a week or two before or after.
- Ultrasound Confirmation: Early ultrasounds (typically between 8-12 weeks) are often used to confirm or adjust the estimated due date, as they can provide a more precise measurement of fetal size.
- Irregular Cycles: If you have very irregular periods, your healthcare provider might rely more heavily on early ultrasound measurements for dating your pregnancy.
Always consult with your healthcare provider for personalized advice and accurate dating of your pregnancy.