WhyUs and Pinn, good luck. "They" say it takes 16 weeks to train for a 1/2-marathon. Also, and I have experience in this, you should be able to run at least 1/2 the marathon distance in advance of your actual marathon. So, in theory, if you can run 6.5 miles, you should be able to complete a 1/2 marathon. However, I would not rest on this and try to get to 8-10 miles before you begin your taper (without injuring yourself, of course). Personally, I would like to reach 10 miles before marathon day, but I will settle for 9.