Calculating your pregnancy due date helps you anticipate your baby’s arrival, plan prenatal care, and track developmental milestones. Most pregnancies last 40 weeks or 280 days from the first day of your last menstrual period (LMP), though only about 4-5% of babies arrive exactly on that date. These four proven methods provide reliable estimates tailored to your situation.
Our free tools simplify the process: use the Due Date Calculator for instant results or the Pregnancy Calculator to monitor weeks and growth stages.
What Is a Pregnancy Due Date and Why Does It Matter?
Your estimated due date (EDD) represents 40 weeks from LMP or 38 weeks from conception. It schedules ultrasounds, screenings, and delivery planning while preventing issues like preterm birth misdiagnosis. Providers often refine initial estimates using ultrasound data for better accuracy.
Quick Start: Input your LMP into our Due Date Calculator for your personalized EDD immediately.
Method 1: Last Menstrual Period (LMP) – The Standard Approach
The LMP method assumes a regular 28-day cycle with ovulation around Day 14. Formula (Naegele’s Rule): Add 280 days to Day 1 of your last period, or subtract 3 months and add 7 days (plus 1 year if needed).
Example: LMP on January 1 gives a due date around October 8 (January 1 plus 9 months plus 7 days).
Best For: Women with consistent cycles. Less reliable for irregular periods or late ovulation.
Try It Now: Our Due Date Calculator handles this calculation automatically with just your LMP date.
Method 2: Conception Date – Ideal for Ovulation Trackers
If you tracked ovulation or know intercourse timing, add 266 days (38 weeks) to the conception date. This accounts for sperm survival (3-5 days) and egg viability (12-24 hours).
Example: Conception on March 15 yields a due date around December 7.
Best For: Couples trying to conceive (TTC) with ovulation kits or apps. More precise than LMP for irregular cycles.
Pro Tip: First determine your fertile window using our Pregnancy Calculator, then compute your EDD.
Method 3: Early Ultrasound – The Most Accurate Option
First-trimester ultrasounds (6-13 weeks) measure crown-rump length (CRL) for ±5-7 day precision, making it the gold standard according to ACOG. It overrides LMP if discrepancies exceed 7 days.
How It Works: Measurements compare fetal size to growth charts, generating gestational age and EDD. Second-trimester scans offer ±7-10 day accuracy.
Best For: All pregnancies, especially irregular cycles or IVF cases.
Refine Your Estimate: Enter ultrasound data into our Due Date Calculator to verify or update.
Method 4: IVF or ART Transfer Date – Lab-Controlled Precision
For assisted reproduction, add days based on embryo age to the transfer date: 263 days for Day 3 embryos, 261 days for Day 5 blastocysts. These dates are exact due to lab timing.
Example: Day 5 transfer on April 1 results in a due date around December 19.
Best For: IVF, IUI, or frozen embryo transfers.
Calculate Instantly: Input transfer details via our Pregnancy Calculator for precise tracking.
Which Method Fits Your Situation? Quick Comparison
| Method | Accuracy | Best For | Recommended Tool |
|---|---|---|---|
| LMP | ±14 days | Regular 28-day cycles | Due Date Calculator |
| Conception | ±7-10 days | Ovulation tracking | Pregnancy Calculator |
| Ultrasound | ±5-7 days | All pregnancies | Due Date Calculator |
| IVF Transfer | ±3-5 days | Fertility treatments | Pregnancy Calculator |
Key Guideline: Prioritize early ultrasound results and consult your doctor.
Frequently Asked Questions About Due Dates
Can my due date change? Yes, about 20% adjust after ultrasound; only 4% deliver exactly on EDD.
Irregular cycles? Opt for conception or ultrasound; start with Period Calculator tracking.
Twins or multiples? Expect earlier delivery by 2-3 weeks.
Over 40 weeks? Induction typically planned at 41-42 weeks for safety
Warning Signs Your Due Date Might Need Adjustment
Big gaps between LMP and ultrasound (>7 days early on), known late ovulation, recent fertility treatments, or mismatched symptoms like delayed heartbeat.
Track Your Entire Pregnancy Journey
Confirm your EDD, then follow weekly progress:
- Get Your EDD: Via Due Date Calculator using your best method.
- Monitor Growth: Use Pregnancy Calculator for trimesters, fetal size, and tips.
- Doctor Visit Prep: Print results to discuss.
Share your LMP or method in comments, and we’ll assist with calculations! Save this for your pregnancy roadmap.