When's the best time to book travel? Depends on the continent: 53 days out for Europe, 162 days out for South America, etc.

That's a chart based on Kayak -- the travel website -- analyzing millions of fare searches and ultimate purchases. It shows the best time to book travel from the United States to the continents described in the chart: so, for example, your best bet for a U.S.-to-Europe trip is 53 days before the trip needs to occur. South America? 162 days. Asia? Almost…