Deciding how much to offer for a home has always been, in part, a guessing game—and today’s uncertain market has made those decisions even more difficult. Now a new online tool at ZipRealty.com quantifies the prevailing spread between asking prices and final sale prices in various city neighborhoods and suburbs. This winter, among areas that had enough sales to make a trustworthy calculation, the site was showing these spreads: At the top of the list were the Near West Side (selling for 107 percent of the asking price); the Loop (104 percent); Bolingbrook (102 percent); and Hoffman Estates (101 percent). At the bottom were Hinsdale, Harvey, West Pullman, and Mundelein (where houses were selling for 93 percent of the asking price); Wilmette (92 percent); Lake Forest (91 percent); and North Chicago (87 percent).