The number of short sales – sales of homes for prices less than what is owed a current mortgage – have spiked in theUnited Statesin the latter part of the year, according to a foreclosure listing firm.

RealtyTrac reported that during the third quarter of this year, short sales by owners behind on their payments jumped 22 percent compared to the same period last year, and sales by owners current on their payment rose by 17 percent. RealtyTrac attributes the flurry of short sales on a tax cut that’s set to expire on Dec. 31.

Currently, the amount of a loan forgiven by banks on a short sale is non-taxable. This was a tax break put in play to help out underwater homeowners, and its elimination could prove costly to those doing short sales.

Depending on what other tax cuts do or don’t expire, a person with $100,000 loan forgiveness on a short sale could wind up owning more than $33,000 in federal income tax if the break isn’t extended.