EDD Calculator
Calculate your estimated due date (EDD) using your last menstrual period, conception date, or IVF transfer date. This pregnancy calculator shows your current week, trimester, and days until delivery.
Pregnancy Details
What is an EDD (Estimated Due Date)?
Your EDD (Estimated Due Date) is the predicted date when your baby will be born. Healthcare providers calculate this date to track pregnancy progress, schedule prenatal appointments, and monitor fetal development through all 40 weeks. The calculation follows Naegele's Rule, developed in the 1800s and still used by obstetricians worldwide as the standard pregnancy dating method.
According to the American College of Obstetricians and Gynecologists (ACOG), only about 4-5% of babies arrive exactly on their EDD. Most babies are born within two weeks before or after this date, which is considered normal. Your EDD helps you plan maternity leave, prepare the nursery, and schedule important prenatal tests like the anatomy scan and glucose screening at the right times. For more pregnancy tracking, try our pregnancy calculator or due date calculator.
How is the Estimated Due Date Calculated?
The EDD calculation depends on which method you use. Each approach has different accuracy levels based on how precisely you know certain dates. Healthcare providers may adjust your EDD after an early ultrasound, especially if measurements differ significantly from the LMP calculation.
Last Menstrual Period (LMP) Method
The LMP method adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a regular 28-day cycle with ovulation occurring around day 14. For example, if your last period started on March 1st, your estimated due date would be December 6th. This is the most commonly used method in obstetric practice.
Formula: EDD = First day of LMP + 280 days
Conception Date Method
If you tracked ovulation or know the exact date of conception, this method adds 266 days (38 weeks) to that date. Since conception happens about 14 days after your last period, this method is more accurate for women who track their fertile window using ovulation prediction kits, basal body temperature, or fertility apps.
Formula: EDD = Conception Date + 266 days
IVF Transfer Date Method
For pregnancies conceived through in vitro fertilization (IVF), the due date calculation is more precise because the exact transfer date is known. The calculation differs based on whether a Day 3 or Day 5 embryo was transferred:
- Day 3 embryo transfer: EDD = Transfer Date + 263 days
- Day 5 embryo transfer: EDD = Transfer Date + 261 days
Pregnancy Week-by-Week Milestones
Understanding what happens each week helps you track your baby's development and know what to expect. Here are the key pregnancy milestones:
| Week | Trimester | Baby Development | Key Events |
|---|---|---|---|
| 4-5 | 1st | Heart begins beating | Pregnancy test positive |
| 8 | 1st | All major organs forming | First prenatal visit |
| 12 | 1st | Fingers and toes developed | First trimester screening |
| 16-20 | 2nd | First movements felt | Quickening begins |
| 20 | 2nd | Halfway point | Anatomy scan ultrasound |
| 24 | 2nd | Viability milestone | Glucose screening test |
| 28 | 3rd | Eyes can open | Third trimester begins |
| 36 | 3rd | Baby drops into pelvis | Weekly checkups begin |
| 37 | 3rd | Full term begins | Group B strep test |
| 40 | 3rd | Fully developed | Estimated due date |
How Accurate is the EDD Calculator?
The accuracy of your estimated due date depends on several factors. Early ultrasound dating (between weeks 8-13) is the most reliable method, with accuracy within 3-5 days. LMP-based calculations are accurate within 5-7 days for women with regular 28-day cycles, but can be off by 2-3 weeks for irregular cycles. IVF dating is highly accurate since the exact embryo transfer date is known.
Research shows that first-time mothers typically deliver 3-5 days after their EDD, while mothers with previous pregnancies often deliver 1-2 days before. About 70% of babies arrive within 10 days of the estimated due date, and 90% arrive within two weeks. If there's more than a 7-day difference between your LMP date and early ultrasound measurements, your healthcare provider will usually adjust your official EDD.
Term Birth Classifications
| Classification | Weeks | Description |
|---|---|---|
| Preterm | Before 37 weeks | May need NICU care |
| Early Term | 37-38 weeks | Most organs mature but some still developing |
| Full Term | 39-40 weeks | Optimal time for delivery |
| Late Term | 41 weeks | Increased monitoring recommended |
| Post-Term | 42+ weeks | Induction typically offered |
Planning Around Your Estimated Due Date
Your EDD helps you schedule important pregnancy milestones. Plan prenatal visits monthly until week 28, bi-weekly from weeks 28-36, and weekly from week 36 until delivery. Key tests include first-trimester screening (weeks 11-14), anatomy scan (week 20), glucose screening (weeks 24-28), and Group B strep testing (weeks 35-37).
Have your nursery ready by week 36 since babies can arrive early. Discuss maternity leave around week 30, pack your hospital bag by week 36, and finalize your birth plan by week 38. Consider childbirth classes between weeks 28-36. For tracking monthly cycles or planning future pregnancies, our ovulation calculator can help identify your most fertile days.
What Happens If Baby Is Overdue?
According to the American College of Obstetricians and Gynecologists (ACOG), if you reach 41 weeks, your provider will increase monitoring and discuss induction options. Most practitioners recommend induction by 42 weeks due to increased risks of stillbirth and complications. Only about 5% of babies arrive on their exact due date.
Last Updated: January 2026 | This calculator provides estimates for educational purposes. Every pregnancy is unique, and your healthcare provider may adjust your due date based on ultrasound findings and individual factors. Consult your doctor or midwife for personalized prenatal care.