[quote="danserr, post:5, topic:226691"]
Two weeks sounds pretty long to me. (asterisk, I am an engaged man and only learning myself with my fiancee).
Here's a link to the Marquette Model of NFP. Go to the NFP Planning user manual or the "quick instructions." They say sperm can live a maximum of 5 days under ideal conditions and an egg one day. So that means a maximum of 6 fertile days per cycle where one can get pregnant, assuming you can accurately know when ovulation occurs. Possibly you might abstain additional days to be safe if it were very desirable to avoid pregnancy, but 2 weeks sounds pretty long.
Your "maximum" is not quite right. You're only taking into account the lifespan of the sperm and the eggs, and not taking into account the fact that you just can't know exactly when the woman is ovulating. There may be a maximum of 6 days on which conception could actually take place, but we cannot identify ONLY those 6 days as fertile by reading a woman's signs of fertility.
In Creighton/Marquette and as far as I know in Billings and sympto-thermal, a woman charts days on which mucus is present as fertile days, up to identifying a peak day. The peak day is not necessarily the day of ovulation--ovulation takes place within a window of 24-48 hours on either side of the peak day, hence the need to abstain in the days prior to the peak when fertile signs are present as well as P+3 days (until the evening of the 4th day after the peak). And you really do need to wait until the evening of the 4th day if you are trying to avoid pregnancy; standard advice to couples using NFP to conceive is to be sure to use days both before and after the peak.
To get to six days of abstinence, then, you have a woman with two days of fertile signs pre-peak, which is not normal (or healthy). I'm trying to remember what "normal" is, and I believe it's at least 5-7 days of fertile mucus--though it could be 8-10. Right there you have two solid weeks of abstinence (10 days pre-peak + 4 days post-peak). Then you'd need to add the heavy and moderate days of menstrual flow as additional days of fertility, so two weeks is probably still about right.
I realize that Marquette uses the ClearBlue monitor to detect ovulation, but even this just measures the LH surge and identifies ovulation as occurring within 24-48 hours before or after the measurement is taken. Not to rain on your NFP parade, but I know at least one couple who trusted the LH surge tests, what they thought they knew about the lifespan of sperm and eggs, and threw out almost all other NFP rules, instead using what they thought was the "actual" window of possible conception: 6 days or so. They conceived--twice--using their reasoning.
Technological innovations that help NFP users are great, but we need to remember the principles at work and the limits of technology.