This provision would reduce corporate taxes by extending net operating loss carryback rules under the stimulus act from two to five years. This means that, for the purpose of taxation, businesses will be able to subtract losses in 2008 and 2009 from profits over the last five years - and in turn recieve a tax refund.  A measure in February's American Recovery and Reinvestment Act increased the carryback loss period from two to five years for small businesses, but this rule now applies to companies of all sizes.

The provision was passed as part of the Worker, Homeownership, and Business Assistance Act of 2009 along with an extension of the homebuyer tax credit and of unemployment benefits.

The provision would cost $33 billion in 2010. However, because it largely defers rather than reduces taxes, it would cost closer to $10 billion over a ten year period. And this cost would be offset -- mainly by delaying, until 2018, a rule to allow the worldwide allocation of interest for the purposes of taxation.