Your pregnancy begins at conception. (Monday, December 31, 2012) Your due date is 266 days (38 weeks) later (Monday, September 23, 2013). We will use the more popular numbering, starting 14 days before your conception. According to this, you are already 2 weeks pregnant at the time of conception, making your total pregnancy last 40 weeks, or 280 days.
An alternative calculation of your due date, based on the Mittendorf-Williams method.
1st day of last period
1. You may come accross various abbreviations for your due date. DD= `Due date`, EDD= `expected date of delivery`, EDC= `estimated date of confinement`
2. We -and probably your doctor too- use Naegeles method (anno 1838) to calculate your due date: Add 280 days to the start of the last menstrual cycle, or 266 days to the ovulation.
3. Your due date is an estimate, it is an average. In the chart below you can see the reality.
In week 38, 2 weeks before the due date, 2 out of 10 women will give birth.
In week 39, 1 week before the due date, 2 out of 10 women will give birth.
In week 40, the due date, 3 out of 10 women will give birth.
In week 41, 1 week after the due date, 2 out of 10 women will give birth.
It is very unlikely that your baby will gestate for longer than 42 weeks. In such cases, estimated due dates may have been incorrectly calculated.
4. A more accurate method to determine the due date is the Mittendorf-Williams Rule This method can also predict the likelihood of premature delivery, which affects 400,000 births annually in the United States. You may try this method yourself using the form above