Don't remember the first day of your last menstrual period (LMP)? You're not alone. Many women aren't sure of their exact date — and that's okay. There are still ways to calculate your pregnancy due date accurately.
The most common method to estimate your due date is by adding 280 days (or 40 weeks) to the first day of your last period. This method is called Naegele’s Rule.
But what if you can't remember your LMP or your periods are irregular?
If you know the day you conceived (for example, via IVF or tracked ovulation), add 266 days to get an approximate due date.
If you were tracking ovulation with ovulation predictor kits (OPKs) or basal body temperature (BBT), estimate your due date by adding 266 days to the date of ovulation.
An early ultrasound (before 13 weeks) is the most accurate way to determine gestational age and your estimated due date. The baby's size is measured and compared with known growth averages.
Try our free due date calculator to get an estimate based on known dates or an assumed cycle length.
For women with irregular cycles, always mention this to your doctor. They may base your due date more heavily on ultrasound results instead of your cycle history.
Even without your LMP, there are still reliable ways to estimate your due date. Whether it’s conception tracking, ovulation tests, or an ultrasound — you’re covered.
🧡 Just remember: due dates are estimates, and only about 5% of babies are born exactly on their due date.
Ready to find your due date? Use our free calculator at duedatenow.online.