Ever wonder where home prices would be today if the real estate market never overheated? Now you can get a clue, thanks to a new online tool from MacroMarkets, the company founded by housing economist Robert Shiller of the Case-Shiller home price index. To crunch the numbers for the application, called the Gap Gauge, the firm assumes that after 2000, when many markets started to bubble, home prices instead simply continued to increase at the same pace at which they had been rising historically. The “gap” is the difference between where the home price index would be sans bubble, and where it actually is today, expressed as a percentage of current prices. The gap for Miami, for example, is 7.1%; though home prices are already down 48% from their peak in that metro area, that gap number indicates they’d have to fall 7.1% further to reach where they’d be if the bubble had never occurred. While a few other cities (such as Boston, Los Angeles and Washington, DC) are also above non-bubble levels, most metro area indexes are below. The gap in Las Vegas, for one, is a negative 34.7%, meaning prices would have to rise by that amount to reach their hypothetical bubble-free levels. Why would post-bubble prices fall so far below where they would be if the real-estate mania had never hit? A likely cause in the case of Las Vegas is the overbuilding that took place in the frenzied market. In the case of Detroit — where prices would have to more than double to reach the levels that MacroMarkets has extrapolated — the implosion of the auto industry is more likely the primary cause of the gap. In any case, you can take a peek at the nationwide average gap, as well as pricing in 20 different metro areas, most of which also can be divided into low-, mid- and high-priced segments of the market. And where will prices go from here? Industry experts are forecasting national home prices will fall 1.4% in 2010, according to a recent MacroMarkets survey of more than 100 economists and analysts. Their five-year outlook is rosier, however; the average expectation is that prices will grow a total of 10.5% by the end of 2014.