Get out your calculator. In one sense, Electoral College math is simple: Add up states’ electoral votes until one presidential candidate’s total is 270 or greater. In another sense, it is complex because there are many ways for each candidate to achieve that sum -- and even some ways for neither to reach 270.

Based on polling data aggregated by the website RealClearPolitics, President Obama has 201 electoral votes safely in the bank. Republican challenger Mitt Romney has 191.