Many websites offer a due date calculator, or pregnancy calculator so as a mums-to-be you can get a pretty good idea of when your baby is due.
The only information you need to put in is the date of your last period and the usual length of your menstrual cycle. Then, hey presto! - a very special date for you to mark on your calendar pops up!
For many centuries women would have been content to know their baby would be born "around Easter" or "in the New Year".
But over the past few decades we've become very good at giving a more accurate "expected date of delivery," or "due date." This enables expectant mums to plan the majority of their pregnancy and allow them to follow the month-by-month advice, knowing what stage she and her baby are at.
However the simple question "When are you due?" can only really be answered by one person, your baby!
And, as useful as it is to look forward to a birthday given by the pregnancy calculator, it's best not to put too much emphasis on a specified date. Fewer than 5 percent of babies actually arrive on the date they are due.
Even a date based on an ultrasound can be off by a week or more depending on the skill of the technician, the timing of the scan and the size of the baby.
Until the end of the first trimester of pregnancy
most babies grow at the same rate but, as pregnancy progresses, fetal size corresponds less and less to the amount of time that the baby is in the womb.
So while scans may reassess a woman's due date throughout her pregnancy, the date actually becomes less accurate as the pregnancy goes on.
If you know the exact date of your last period you can use a due date calculator
But of course this too can only give an expected date. Your baby may have other ideas!
If you go past your due date (and many women do) just count it as more time to establish a bond with your baby, for her to become fully equipped to face the world and give you the chance to get your home ready for her arrival.
It may be best to be a little vague, telling friends and family that baby is due "sometime in June" rather than on a specific date in order to prevent too many people calling you and "sympathising" when baby is "late".