How to Estimate Your Due Date

Learn how to estimate when your baby will arrive.

During your menstrual cycle, every month typically 14 days after the first day of your last period, an egg will be released. Generally there is a window of 24-48 hours for sperm to fertilise the egg. This is the reasoning that is behind your due date calculations. However, Please keep in mind that your due date is only an estimate. Quite often, especially with first time mothers, your child can deliver up to two weeks after your expected due date. We can help you make a basic estimate of when your baby will be due, however, your midwife or health adviser may tell you an alternate date. This date may again change after you have your first scan. During your first scan your midwife will be able to estimate more accurately your expected due date by measuring how big your baby is.

The customary way of calculating your expected due date is to count 280 days ahead from the first day of your last menstrual cycle. This works on the basis that an average term of pregnancy lasts 266 days. 14 days are then added to this figure to represent when your most fertile period would have been and therefore when you were most likely to conceive. A slightly easier way of calculating your expected due date is to add 7 days to the first day of your last period and subtract three months.

However, the notion that you conceived exactly 14 days after the first day of your last menstrual cycle is only a basic general marker and is by no means accurate. This can vary due to a number of reasons, for instance if your menstrual cycle is generally longer or shorter than 28 days.

Other methods of working out your expected due dates are.

1. Working out the date from time of intercourse.
2. Testing the human chorionic gonadotropin levels in your blood. This is done at the hospital. Generally levels are at least 5 mIU/ml in early pregnancy, and this level doubles approximately every two days.
3. When pregnancy symptoms first began, for instance, tender breasts, morning sickness.

There is no totally accurate way of telling when your baby will arrive. All you can do is be prepared, patient and allow nature to take its course.