Due Date Calculator
Professional, accurate, and personalized pregnancy tracking.
How is your Due Date Calculated?
Most healthcare providers use Naegele’s Rule, which estimates your due date by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). However, this assumes a perfect 28-day cycle. Our advanced calculator allows you to adjust for your unique cycle length and luteal phase for better accuracy.
The Mittendorf-Williams Rule
Research by Mittendorf and Williams suggests that the average pregnancy actually lasts slightly longer than 40 weeks, especially for first-time mothers. Our “Advanced Health Factors” option incorporates these findings, considering your age, ethnicity, and parity to provide a more realistic window for your baby’s arrival.
IVF and Ultrasound Dating
If you conceived via IVF, your due date is calculated based on the embryo transfer date and the age of the embryo (typically Day 3 or Day 5). For those with irregular cycles, an ultrasound scan measuring the Crown-Rump Length (CRL) is often the most reliable method during the first trimester.
Frequently Asked Questions
While no calculator can predict the exact day of birth, our tool uses advanced algorithms including the Mittendorf-Williams rule, which is shown to be more accurate than standard methods by accounting for individual health factors.
If your cycles vary, we recommend using the “Ultrasound” method or the “Conception Date” method if known. Ultrasound measurements in the first trimester are considered the gold standard for dating irregular pregnancies.
It can! Your doctor might adjust your due date after a dating ultrasound if the baby’s size differs significantly from the LMP-based estimate.