Calculating your pregnancy due date is basically a piece of simple arithmetic based on the date of the first day of your last period and the average length of your menstrual cycle.
On the assumption that you've got this information handy, all that's then required is to add 40 weeks to the first day and, hey presto, you've got your pregnancy due date - well near enough to be within a few days either side in most cases.
Incidentally, a baby born only 3 weeks earlier than the official pregnancy due date is classified as being premature although babies born as little as 24 weeks after conception are still considered to be viable given the full resources of modern medical care available in Western societies.
However, in practice 92% of babies very obligingly arrive within a two to three week window around their predicted pregnancy due date.
So, on the face of it everything seems to be hunky-dory - you've got your pregnancy due date either by calculating it yourself (NOT recommended except for initial guidance) or, much better, by being informed of it by your Doctor after other relevant factors are taken into account.
There are also numerous websites where you can just enter your dates (first day of your last period is the most important) and get an instant calculation of your pregnancy due date.
Then all you have to do (in theory!) is to wait for your baby to politely keep the appointment set for him or her.
The only problem is that not everyone may be well enough organised to know the date when her last period started or the average length of her menstrual cycle.
But not to worry if your dates are a couple of weeks adrift. The prediction of your pregnancy due date may well be wrong when you are first given it but as your pregnancy progresses other signs and symptoms will start to indicate that a different date is more likely.
So pretty soon you will be able to be quite certain that, provided your baby is one of the 92% who arrive more or less on time, you will be giving birth somewhere around the date given.
But these calculations also potentially have a hidden benefit if you are still at the stage of planning your family because you can use simple arithmetic again to predict when during your menstrual cycle you are most likely to conceive.
The same information used to predict the pregnancy due date is also used for this prediction as it is based on the first day of your period together with the average length of your cycle with the well established assumption that you are most likely to ovulate within a time frame of 2 to 3 days either side of the middle of this period of time.
So if your cycle is 28 days and your first day was the first of the month, the best time to have sex would be between the 12th and 16th of the month although there's no need to unnecessarily restrict yourself to just this window of opportunity!
And if you and your partner are both fortunate enough to be in your twenties, you have a 20-25% chance of getting pregnant during each month that you're trying, so 4 or 5 months could easily do the trick!
If you're really confident, you could even draw up a little chart of likely pregnancy due dates, although that may be tempting Providence a bit too far!
Obviously, as people get older, the likelihood of such spectacular early success starts to diminish, but statistics show that eventually 95% of all couples who try to start a family finally succeed even if it seems to take for ever for that all important pregnancy due date to be finally announced!
In fact, on average, one couple in five has failed to conceive after 12 months of trying so don't be too worried if things don't seem to be working out quite as quickly as you may have hoped.
If you want to check your potential pregnancy due date online, it is very simple to do so via a Google search for instance, but please be advised that there is no substitute for proper medical advice. Many of these sites will also allow you to calculate when you are likely to ovulate during your monthly cycle.