I run 4 miles a day. Every now and again, once or twice a week, I do a long run at the weekend. Just build up the long run: first 5 miles, then 6 miles, then 7 and so on.
I managed to reach 12 miles pretty quickly and I am sure I could do 13. I find having a good base is the best thing to do. In other words, as long as I keep running my daily short 4 mile runs I can bang out a long run when I need to without having to train for it (as long as I have run that distance before).
The other issue I find with runs over, say, 8 miles is that you do start to ache and tire in places you may not be used to. So once you reach the higher distances expect to go home, eat and sleep.
Last edited by IanG; 10-18-2014 at 07:11 PM.