Estimated Due Date Calculator
Choose your method, enter your dates, and get your estimated due date (EDD), current gestational age, and key pregnancy milestones.
This calculator provides estimates only and does not replace advice from your OB-GYN or midwife.
How an Estimated Due Date Is Calculated
An estimated due date (EDD) is a best-guess prediction of when labor may begin. Most pregnancies are tracked as 40 weeks from the first day of the last menstrual period (LMP), not from the day of conception. Because ovulation usually occurs about two weeks after LMP in a 28-day cycle, this convention gives healthcare teams a standard way to track fetal development.
Naegele's Rule (Most Common Method)
If your cycle is close to 28 days, a classic formula called Naegele's Rule is used:
- Take the first day of your last period
- Add 1 year
- Subtract 3 months
- Add 7 days
In practice, this is the same as adding 280 days to your LMP. If your cycle is longer or shorter than 28 days, the estimate can be adjusted by the cycle-length difference.
Conception-Based and IVF Dating
If conception date is known, estimated due date is generally: conception date + 266 days. For IVF pregnancies, transfer date and embryo age provide a more precise baseline. This is why IVF due dates are often very accurate early on.
Why Your Due Date Is an Estimate, Not a Deadline
Despite the name, a due date is not a guaranteed delivery day. Most births occur within a window around the EDD. It is perfectly normal for labor to begin a little earlier or later. Only a small percentage of people deliver exactly on their due date.
- Ovulation may happen earlier or later than expected
- Implantation timing varies
- Cycle regularity affects dating accuracy
- Early ultrasound may revise the estimate
How to Use This Calculator Correctly
For the best estimate, use the method that matches what you know:
- LMP method: Best when periods are reasonably regular.
- Conception method: Helpful when conception date is known confidently.
- IVF method: Most precise for assisted reproduction cycles.
After calculation, compare your result with your provider's dating ultrasound. In many prenatal clinics, first-trimester ultrasound is considered the most accurate way to establish gestational age.
Pregnancy Milestones You Can Track
Once you know your estimated due date, it becomes easier to organize prenatal care and planning. Common milestones include:
- End of first trimester (around 13 weeks, 6 days)
- Start of second trimester (14 weeks)
- Anatomy scan window (usually around 18–22 weeks)
- Start of third trimester (28 weeks)
- Term pregnancy period (around 37 weeks onward)
Frequently Asked Questions
Can I trust an online due date calculator?
Online calculators are useful for quick estimates, but they do not replace professional care. Your OB-GYN or midwife may refine your date based on ultrasound and clinical findings.
What if I have irregular periods?
If your cycles are irregular, LMP-based estimates can be less accurate. In that case, early ultrasound is often the best way to confirm dating.
Does cycle length really matter?
Yes. A person with a 33-day cycle may ovulate later than someone with a 28-day cycle. Adjusting cycle length helps improve LMP-based estimates.
Can due date change after my first appointment?
It can. If first-trimester ultrasound measurements differ meaningfully from menstrual dating, your provider may update your estimated due date.
Final Note
This estimated due date calculator is designed for education and planning. Use it to understand your timeline, but always follow your clinician's guidance for prenatal testing, appointments, nutrition, and labor planning.