Pregnancy Due Date Calculator: Estimated Delivery Date (EDD)
Expecting a new baby? The Pregnancy Due Date Calculator estimates your baby’s expected delivery date (EDD) and current gestational age in weeks and days using the clinically recognized Naegele’s Rule based on your last menstrual period (LMP) or ultrasound conception date.
How to Use the Pregnancy Due Date
Follow these simple steps to calculate your exact result in seconds.
Select Calculation Method
Choose Last Menstrual Period (LMP) or Conception Date.
Enter Date
Select the first day of your last period (or date of conception/IVF transfer).
Set Average Cycle Length
Default is 28 days; adjust if your natural menstrual cycle is longer or shorter.
View Due Date & Trimesters
Instantly see your estimated due date, current gestational week, and trimester timeline.
How the Calculation Works
Understand the underlying formula and arithmetic logic.
Core Formula
Naegele’s Rule: Due Date = First Day of LMP + 1 Year - 3 Months + 7 Days (Adjusted for cycle length)
A standard human pregnancy lasts approximately 280 days (40 weeks) from the first day of the last menstrual period. Because ovulation typically occurs 14 days before the next period, the tool adds (Cycle Length - 28) days to adjust for individual cycle variance.
Edge Cases and Special Rules Handled
Irregular or Long Menstrual Cycles
If your cycle is 35 days instead of 28, ovulation occurred approximately 7 days later. The tool adds 7 days to the 280-day baseline to prevent premature induction concerns.
IVF Embryo Transfer Timing
For in vitro fertilization (IVF), a 3-day embryo transfer adds 263 days from transfer, while a 5-day blastocyst transfer adds 261 days.
Real-World Examples & Calculations
See step-by-step walkthroughs of common situations.
Standard 28-Day Cycle LMP Calculation
Context: An expectant mother had the first day of her last period on May 10th with a standard 28-day cycle.
Calculation: May 10 + 280 days = February 14th of the following year.
Long 34-Day Menstrual Cycle
Context: An expectant mother with a 34-day cycle has an LMP of June 1st.
Calculation: June 1 + 280 days + 6 days = March 14th.
Comprehensive Guide: Practical Concepts & Deep Dive
Topical insights, industry conventions, and real-life guidelines.
The Clinical Basis of Naegele’s Rule
Formulated by German obstetrician Franz Karl Naegele in the early 19th century, Naegele’s rule calculates an estimated delivery date by counting 280 days (40 full weeks) from the first day of the last normal menstrual period.
The rule assumes a standard 28-day cycle where ovulation and fertilization occur around day 14. If a woman has a 35-day cycle, ovulation likely occurred on Day 21 (14 days before the next expected period). Accounting for this 7-day shift ensures doctors and midwives don’t falsely categorize the pregnancy as overdue.
The 3 Trimesters of Pregnancy
Pregnancy is divided into three trimesters: The First Trimester (Weeks 1 through 13) encompasses embryo implantation, heart formation, and initial organ development. The Second Trimester (Weeks 14 through 27) is often called the "golden trimester" as morning sickness subsides and fetal movements become noticeable.
The Third Trimester (Weeks 28 through 40+) focuses on fetal lung maturation, rapid brain development, and preparing the body for labor.
Common Mistakes to Avoid
Avoid these frequent calculation pitfalls that lead to errors.
✕Assuming the baby MUST arrive on the exact due date
Why it happens: Can cause unnecessary anxiety when delivery doesn’t happen on that precise day.
✓Solution: Only 4-5% of babies arrive on their exact due date; anywhere between 37 and 42 weeks is considered normal full-term.
Pregnancy Trimester Milestone Schedule
Week-by-week timeline of pregnancy trimesters and fetal development.
| Trimester | Gestational Weeks | Duration | Major Fetal Milestone |
|---|---|---|---|
| First Trimester | Weeks 1 to 13 | 13 weeks | Heartbeat detected, major organs formed |
| Second Trimester | Weeks 14 to 27 | 14 weeks | Fetal movement felt, gender anatomy scan (wk 20) |
| Third Trimester | Weeks 28 to 40 | 13 weeks | Rapid weight gain, lung surfactant development |
| Full Term Window | Weeks 37 to 42 | 5 weeks | Baby fully mature for safe delivery |
Comparison vs Alternative Calculation Methods
Why dedicated online calculation saves time and prevents errors.
Adjusting for individual cycle length provides a far more accurate estimated due date than rigid 28-day wheels.
| Method | Speed | Accuracy | Convenience | Practical Notes |
|---|---|---|---|---|
TimeCalculatorHubRecommended | Instant | High (Naegele’s rule + cycle adjustment) | Includes trimester milestones | Accounts for irregular cycle lengths |
Standard Paper Pregnancy Wheel | Fast | Assumes strict 28-day cycle | Used in doctor clinics | Can be off by a week for 35-day cycles |
First Trimester Ultrasound | Clinical | Gold standard (accurate within 3-5 days) | Requires clinical appointment | Measures crown-rump length (CRL) |
TimeCalculatorHub
RecommendedStandard Paper Pregnancy Wheel
First Trimester Ultrasound
Practical Tips for the Pregnancy Due Date
Expert advice and helpful shortcuts tailored to this tool.
Only About 4-5% of Babies Arrive on Their Exact Due Date
A due date is an estimate; full-term pregnancy is considered anywhere between 37 weeks and 42 weeks.
Track Trimester Milestones
First trimester ends at Week 13; second trimester spans Weeks 14–27; third trimester begins at Week 28.
Frequently Asked Questions
Clear, honest answers to common questions about this calculator.