If you have a look on fertility friend you can do a search to see all charts where the timing is pretty much right (you can tick days when intercourse took place on O-3, O-2, O-1, O, O+1.
I did a little analysis (I was having a quiet day at work and am getting a bit obsessive about trying for a new baby!!!). Embarrassing as it is am going to share it with you.
For those who timed it right and hit all five of those days about 41% got pregnant and another 4% had 'chemical pregnancies' ie early miscarriages. The statistics were relatively similar if you only hit O-2, O-1 and O (39% pregnant, 4% miscarriage). Or similarly with O-1, O and O+1 it was 37% pregnant, 4% miscarriage).
So assuming that the population on Fertility Friend is similar to the general population you actually have a pretty good chance of being pregnant within 6 cycles if you manage to time it right each cycle. By my reckoning if 100 women try for a baby getting the timing right each cycle, with a 41% chance each cycle of ending up pregnant, by the end of 6 cycles 95 of those women will be pregnant.
In fact it is likely that the Fertility Friend population is slightly less fertile than the general population, because many women will only think about going on such a website if they have experienced difficulties getting pregnant. Also some of those women will have multiple cycles stored on fertility friend whereas the most fertile will have less cycles, because they got pregnant quickest. So the total collection of cycles stored in their database is slightly skewed to the less fertile.
Finally, I wondered how much age makes a difference to the chance of conceiving IF you time it right. I filtered by age in three year blocks (22 - 24, 24 - 26, etc etc up to 46.) As you would expect there is a reduction in your chances as you get older. Up until the age of 30 there was essentially little drop-off, with your chance being around 40 - 44%. At age 33 your chance is reduced to around 36%, and by age 29 your chance is around 33%. By the age of 43 you have around a 19% chance of getting pregnant IF you time intercourse correctly around ovulation.
Clearly all this depends on a woman actually ovulating and being able to determine the timing of ovulation. These statistics only included cycles where an ovulation date was determined.
Hope this is of interest to someone! If not, I am heartily embarrassed.