I'm a member of New York Road Runners and have attended some of their classes on running the marathon. They have a pretty comprehensive schedule on the New York Road Runners website that tells you how much to run on a daily basis starting 18 weeks before the marathon. The last three weeks you taper off. Your longest run is three weeks before the marathon. At the schedule I'm looking at it says 3 miles the day before the race. There are different schedules on their for different levels and if you have modane marathon injuries like shin splints and tight IT Band you want to heal up before the big race. I'm training again for the marathon but not following the schedule exactly - I'm taking it a little easy on my bod and mixing in some cross training. The long runs I'm doing for sure but the really long ones like 18 and 20 I'm giving myself a week off of a long run in between. I'm only going to do 2 or 3, 20 miles plus before the big day. I'm trying to beat the 4 hour mark so it's different for everyone and their goal.