The standard method of calculating your due date is to add 280 days to the fist day of your last menstrual period, or LMP.
Enter the first day of your last menstrual cycle below:
How this concept works: the 280-day cycle works on the typical 266-day gestation period plus 14 days, which would be the time from when you had your first day of your period, until the time when you would have more than likely ovulated. So you see this is not exact science. Why? Well, because this method assumes you would have ovulated exactly 14 days after you started your period and it assumes fertilization took place on that exact day.
There are other methods of calculating your due date of course. If you had been keeping track of your basal body temperature or your LH surge, you would know when ovulation occured, when you had intercourse and the date of conception. If you know this exact date for sure, then you would simply add the 266-day typical gestation period, and you would have your due date. Alternatively, you could use software which will not only track your ovulation cycle but also give you an estimated due date once you are pregnant.
Unfortunately there is no exactly perfect way of determining when your little bundle of joy will arrive. But that doesn't mean you can't have some fun with this uncertainty. Consider creating a pregnancy pool so all your friends and family can guess just when they think your little one will arrive.
And remember: your due date may seem like a long way off at the beginning, but your baby will arrive sooner than you think.
