For now, Democrats are most likely going to win three to four seats. How did I get to those numbers? I summed up Democrats’ chances in all 34 seats.

For each seat, I estimated the chance that the Democrat or Republican would win. That percentage chance comes from a simple model based on an analysis of Senate races since 2006. For seats in states where polling has been done this year, the model includes variables for an average of all polls in the state since January,1 how Democratic- or Republican-leaning the state was in the previous presidential election (2012 for this year), whether the incumbent is running for re-election, and the average generic ballot result2 nationwide since January to give us an idea of the national environment. Where there are no polls, the model is the same except without a polling variable. This makes the model less certain about the outcome but still gives us a rough guide.