For taxable years beginning on or after July 1, 2012, but before July 1, 2014, retail companies are required to determine their Virginia taxable income by using an apportionment formula with a triple-weighted sales factor.  A single sales factor apportionment formula will be phased in over a three-year period beginning as a triple-weighted sales factor, followed by a quadruple-weighted sales factor, and then a single sales factor for taxable years beginning on and after July 1, 2015.