It varies. It varies mostly by female age, and is highest in your 20's and drops exponentially after age 37. The miscarriage rate rises with age, too.
It depends. It depends on women's age and what method do you use to achieve pregnancy. If you are young and healthy, and you ask what is the chance you can achieve pregnancy each cycle, then the answer is about 20%. If you ask for a 34 year old woman with infertiity, the chance of getting pregnant by IUI or ivf, the answer is 15% and 55% respectively (it also depends on the cause of infertility).
10 - 25% . The figure oft quoted is 85% of women will conceive within 12 months of unprotected intercourse. As women age the success rate to achieve pregnancy declines - from approx. 20 - 25% per cycle for a women in her 20's to approx. 10-15% per cycle in her late 30's. This, of course, is in the absence of any detectable cause for infertility - ie, abnormalities in cycle, sperm, or tube/uterus.