Due Date Calculator
Find out when your baby is due using your last menstrual period, conception date, or IVF transfer date. Our calculator uses medically accepted methods including Naegele's rule.
How the Due Date Calculator Works
Method 1: Last Menstrual Period (LMP)
This method uses Naegele's rule, the standard formula used by healthcare providers worldwide. It adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day menstrual cycle with ovulation on day 14.
Method 2: Conception Date
If you know when you conceived (or ovulated), this method adds 266 days (38 weeks) to that date. Since conception typically occurs about 14 days after the start of your period, this gives the same result as the LMP method when ovulation occurred on cycle day 14.
Method 3: IVF Transfer Date
For IVF pregnancies, the embryo transfer date is used. The formula adds 266 days minus the embryo age at transfer. For a Day 5 (blastocyst) transfer, it adds 261 days. For a Day 3 transfer, it adds 263 days.
Frequently Asked Questions
How is my due date calculated from my last period?▾
Your due date is calculated using Naegele's rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes an average 28-day cycle with ovulation occurring on day 14.
How accurate is a due date calculator?▾
Due date calculators provide an estimate. Only about 5% of babies are born on their exact due date. Most babies arrive within two weeks before or after the estimated due date. Ultrasound dating in the first trimester is generally considered the most accurate method.
How is the due date different for IVF pregnancies?▾
For IVF pregnancies, the due date is calculated from the embryo transfer date. The formula adds 266 days minus the embryo age at transfer (3 or 5 days) to the transfer date, since the exact fertilization date is known.
Can my due date change during pregnancy?▾
Yes. If an early ultrasound shows a significant difference from the LMP-based due date (more than 5-7 days), your healthcare provider may adjust your due date based on the ultrasound measurements.
What is Naegele's rule?▾
Naegele's rule is a standard method for estimating the due date. It calculates the expected delivery date by adding 280 days (or 40 weeks) to the first day of the last menstrual period. It was named after German obstetrician Franz Karl Naegele.
Medical Disclaimer
This calculator is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider for medical decisions regarding your pregnancy.