According to the "Simple Due Date Calculator" in my "Taking Charge of Your Fertility Software":
If you ovulate and conceive on this date... Wednesday, February 01, 2006
Your due date will be... Wednesday, October 25, 2006
If you ovulate and conceive on this date... Wednesday, February 15, 2006
Your due date will be... Wednesday, November 08, 2006
***
According to the "Fertility Planner" in my "Taking Charge of Your Fertility Software":
If I want to deliver a baby on or around Sunday, November 05, 2006
I need to conceive around... Friday, February 10, 2006
... and based upon my own cycle history, I should plan on having intercourse between... February 5, 2006 and February 12, 2006
... and, if successful, my delivery range could be expected to be between... October 24, 2006 and November 13, 2006
... and my due date would be... Friday, November 03, 2006
***
Documentation from the software explaining how the above information was calculated:
Delivery Planning Tab:
This tab helps you plan your next pregnancy. You simply select a desired delivery date from the drop-down calendar and TCOYF calculates when you will need to conceive in order to have a baby near your desired date. The reason you may not be able to deliver on the exact date you desire is that it your due date is determined by your conception date, and your conception date is determined by when you ovulate. TCOYF estimates your ovulation date using your cycle history, projecting your delivery date from this information.
The dates you should have intercourse are also shown. Because conception can result from intercourse occurring up to 5 days prior to ovulation, TCOYF recommends having intercourse for each of the 5 days preceding the estimated conception date and for the 2 days following it, just to be safe. Unless your partner has a low sperm count or some other medical condition that prevents it, intercourse is recommended on each of the 5 days preceding ovulation, and on the ovulation day itself, to maximize your chances of achieving pregnancy.
TCOYF also shows the estimated delivery range. If you conceive on the estimated ovulation date, you have a 75% chance of delivering your baby within this range.
The due date is calculated by adding 266 days to the conception date. This is because the average human gestational length is 266 days.
If you check the Show planning dates in Calendar box TCOYF will highlight the recommended intercourse dates, the conception date, and the delivery range and due date by means of colors and icons in the Fertility Calendar. This information will not show up in the Fertility Chart, however. If the conception date is for a day in the past, or if you are currently pregnant, this option will be disabled and you will not be able to show these projections in your Calendar.
These projections can change during the course of your cycle based upon new information, such as a change in your average cycle length or average luteal phase length. This is normal behavior and is intentional, as TCOYF tries to make the best educated guess it can using the most accurate data.
If you elect to override the use of your own history under the Cycle Forecasting tab, those same overrides will be applied to these calculations, as well.
The Simple Due Date Calculator button brings up a quick due date calculator that ignores your cycle history and lets you pick either a conception date or due date, and it calculates the other."
***
It's not as "cut 'n dry" as people would have you expect. ;)