Due date calculator
Due Date Calculator — Estimate Your Pregnancy Week and Baby’s Arrival Date
The Due Date Calculator helps determine when your baby is likely to be born by estimating your Estimated Due Date (EDD). This online tool is based on the Last Menstrual Period (LMP)Naegele’s Rule — the most common method used by doctors worldwide.
How the Due Date Is Calculated
Pregnancy typically lasts about 280 days (40 weeks) from the first day of your last menstrual period. If you know your ovulation or conception date, your due date is estimated by adding 266 days (38 weeks). Women with longer or shorter cycles can use an adjusted version of the formula:
Adjusted Formula: EDD = LMP + (280 + (CycleLength − 28)) days
Calculation Methods Supported
- LMP method: Adds 280 days to the first day of your last period.
- Conception method: Adds 266 days to your conception date.
- Ultrasound-based method: Uses fetal measurements for more accurate results during early pregnancy.
Why the Due Date May Vary
Only about 4–5% of babies are born exactly on their predicted due date. Most deliveries occur within two weeks before or after the calculated EDD. Factors such as hormonal balance, ovulation timing, irregular menstrual cycles, and fetal growth patterns can affect the actual delivery date.
Pregnancy Trimesters Explained
- 1st Trimester (Weeks 1–12): Fertilization, implantation, and organ development occur.
- 2nd Trimester (Weeks 13–26): The fetus grows rapidly, and most mothers begin to feel movement.
- 3rd Trimester (Weeks 27–40): The baby gains weight and prepares for birth.
Accuracy and Medical Validation
While Naegele’s Rule offers a reliable estimate, doctors often confirm due dates using a first-trimester ultrasound. This method is accurate within ±5–7 days and helps adjust for irregular cycles or uncertain LMP dates. Our calculator aligns with recommendations from medical organizations such as:
- American College of Obstetricians and Gynecologists (ACOG)
- Centers for Disease Control and Prevention (CDC)
- World Health Organization (WHO)
- PubMed: Gestational Age Assessment Methods
Why Use This Calculator
This tool does more than estimate your delivery date. It also shows your current gestational age and trimester progress. You can use it to plan prenatal visits, monitor fetal development, and prepare for your baby’s arrival. Please note that this calculator is for educational purposes only and should not replace professional medical advice.
References and Sources
