You're pregnant — congratulations! One of the first questions on your mind is: When is the baby coming? The estimated due date (EDD) gives you an orientation for the next 40 weeks of pregnancy.
In this guide, you'll learn how to calculate your due date from three different starting points — last menstrual period, conception date, or IVF transfer — and what the results mean for your pregnancy journey.
Three Ways to Calculate Your Due Date
Depending on what information you have, there are three methods to determine your due date. Our due date calculator supports all three.
1. Last Menstrual Period (LMP Method)
The most common method. You need the first day of your last period and your average cycle length. Using Naegele's rule: LMP + 280 days (for a 28-day cycle). Cycle length adjustments shift the date earlier or later.
2. Conception Date
If you know the exact date of conception, the calculation is: Conception date + 266 days (38 weeks). This method is more precise because it doesn't rely on estimating when ovulation occurred.
3. IVF Transfer Date
For IVF pregnancies, the embryo transfer date is known precisely. Since the embryo is already 3 or 5 days old at transfer: Day-5 transfer: + 261 days — Day-3 transfer: + 263 days.
What Is Naegele's Rule?
Naegele's rule is the most widely used method for estimating a due date. Developed by German gynecologist Franz Naegele in the 19th century, it assumes a 28-day cycle with ovulation on day 14.
Naegele's Formula
First day of last period + 7 days − 3 months + 1 year
Equivalent to: LMP + 280 days (40 weeks)
If your cycle differs from 28 days, the EDD shifts accordingly: a 30-day cycle pushes the date 2 days later; a 26-day cycle moves it 2 days earlier. Our due date calculator handles this adjustment automatically.
Calculate Your Due Date Now
From LMP, conception date, or IVF transfer — free and instant.
Calculate for free →Gestational Weeks and Trimesters
Pregnancy is typically divided into 40 weeks counted from the LMP, organized into three trimesters:
1st Trimester (Weeks 1–12)
All organs form. A heartbeat is detectable by week 6. The risk of miscarriage drops significantly after week 12.
2nd Trimester (Weeks 13–27)
Rapid growth. First movements felt. Anatomy scan at week 20. Gender becomes visible. Most pregnant people feel best in this phase.
3rd Trimester (Weeks 28–40)
Baby gains weight and matures. Lungs develop fully. From week 37, the baby is considered full term.
Key Pregnancy Milestones
- Week 6: Heartbeat visible on ultrasound
- Weeks 8–10: First prenatal visit, blood tests, first ultrasound
- Week 12: End of critical first trimester — miscarriage risk falls
- Week 20: Anatomy scan — detailed organ check
- Week 24: Viability threshold with intensive neonatal care
- Week 28: Start of third trimester
- Week 37: Full term — birth is medically uncomplicated
- Week 40: Estimated due date (EDD)
Why the EDD Is an Estimate
Only about 4% of babies are born exactly on the estimated due date. Most arrive within a window of two weeks before to two weeks after the EDD. The main reasons:
- The exact moment of ovulation is rarely known with precision
- Cycle length varies between individuals and from cycle to cycle
- First pregnancies tend to run slightly longer on average
- Genetics and individual physiology influence pregnancy length
- Naegele's rule is based on 19th-century population averages
Related Calculators
More tools for fertility and pregnancy planning:
- Pregnancy Calculator — Track milestones, trimesters, and progress of your pregnancy
- Ovulation Calculator — Find your fertile window and predict ovulation day
Summary
Your due date is an important reference point, not a fixed deadline. Our due date calculator supports all three calculation methods and shows you trimesters, countdown, key dates, and milestones at a glance. Every pregnancy is unique — trust your body and your care team.
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