Due Date Calculator
Calculate your estimated due date and get a complete pregnancy timeline with important milestones. Our calculator uses medically-approved methods to provide accurate estimates based on your last menstrual period or conception date.
Calculate Your Due Date
Understanding Your Due Date
What is a Due Date?
Your estimated due date (EDD) is calculated as 280 days (40 weeks) from the first day of your last menstrual period. This is based on the average pregnancy length, though normal pregnancies can range from 37-42 weeks.
How Accurate Are Due Dates?
Only about 5% of babies are born exactly on their due date. Most babies (85%) are born within 2 weeks before or after the estimated due date. Your due date is best thought of as a "due month" rather than a specific day.
Why Due Dates Matter
Due dates help healthcare providers schedule important tests, monitor fetal development, and determine if interventions are needed. They also help you prepare mentally and practically for your baby's arrival.
Calculation Methods Explained
Last Menstrual Period (LMP) Method
This is the most common method used by healthcare providers:
- Adds 280 days (40 weeks) to the first day of your last period
- Assumes a 28-day cycle with ovulation on day 14
- May be less accurate for irregular cycles
- Widely used because it's easy to remember your last period
Best for: Women with regular 28-day cycles who remember their last period date.
Conception Date Method
Based on the actual or estimated conception date:
- Adds 266 days (38 weeks) to the conception date
- More accurate if you know when you ovulated
- Useful for IVF pregnancies or tracked ovulation
- Accounts for non-standard cycle lengths
Best for: Women who track ovulation or had assisted reproduction.
Ultrasound Dating
Uses fetal measurements to estimate gestational age:
- Most accurate method, especially in first trimester
- Based on fetal size and development
- Accounts for individual variation
- May override LMP dating if significantly different
Best for: Uncertain LMP dates or irregular cycles.
Pregnancy Timeline Overview
First Trimester (Weeks 1-12)
Key developments:
- Major organ formation
- Heart begins beating
- Neural tube closes
- Limb buds appear
Common symptoms: Morning sickness, fatigue, breast tenderness
Important appointments: First prenatal visit, initial screening tests
Second Trimester (Weeks 13-27)
Key developments:
- Gender determination possible
- Quickening (first movements)
- Organ maturation
- Hair and nail growth
Common symptoms: Energy returns, growing belly, backaches
Important appointments: Anatomy scan, glucose screening
Third Trimester (Weeks 28-40)
Key developments:
- Rapid brain development
- Lung maturation
- Weight gain acceleration
- Positioning for birth
Common symptoms: Shortness of breath, frequent urination, Braxton Hicks
Important appointments: Growth monitoring, Group B strep test
Important Pregnancy Milestones
Due Date Calculator FAQ
What if I don't remember my last period?
If you can't remember your last menstrual period, your healthcare provider will likely use ultrasound dating. Early pregnancy ultrasounds (before 10 weeks) are most accurate for dating purposes.
Can my due date change?
Yes, your due date may be adjusted based on ultrasound measurements, especially if there's a significant difference from your LMP-based date. Generally, only one due date change is made during pregnancy.
What if my cycle is longer or shorter than 28 days?
Our calculator accounts for different cycle lengths. If your cycle is consistently different from 28 days, this affects your ovulation timing and, consequently, your due date calculation.
When should I contact my healthcare provider?
Contact your healthcare provider as soon as you suspect you're pregnant, even before calculating your due date. They can confirm pregnancy and begin appropriate prenatal care.