Pregnancy Due Date Calculator
Estimate your baby's arrival and track your progress
How Your Due Date is Calculated
Most pregnancies last approximately 40 weeks (280 days) from the first day of your last menstrual period (LMP). Our calculator uses the standard Naegele's Rule but adds a custom adjustment for your specific menstrual cycle length to provide a more personalized estimate.
Understanding the Math
The standard calculation assumes a 28-day cycle. If your cycle is longer than 28 days, you likely ovulated later, meaning your due date will be slightly later. Conversely, a shorter cycle usually results in an earlier due date. The formula we use is:
- Standard Due Date = LMP + 280 days
- Adjusted Due Date = Standard Due Date + (Average Cycle Length – 28 days)
Example Calculation
If your last period started on January 1st and you have a 30-day cycle:
- Base 40 weeks: October 8th.
- Cycle adjustment: Since 30 days is 2 days longer than the average 28, we add 2 days.
- Final Estimated Due Date: October 10th.
Why the Due Date is an Estimate
It is important to remember that a due date is just an estimate. Only about 4% of babies are born exactly on their predicted due date. Most babies arrive between 37 and 42 weeks of pregnancy. Factors such as maternal health, fetal development, and genetic history can all influence the actual delivery date.
Medical Disclaimer: This tool is for informational purposes only and does not replace professional medical advice. Always consult with your OB-GYN or midwife to confirm your due date through clinical examinations or ultrasound dating.