The Pay It Back Act amends the Emergency Economic Stabilization Act of 2008 (EESA) to revise the limitation on the authority of the Secretary of the Treasury to purchase troubled assets under the Troubled Asset Relief Program (TARP) to $700 billion outstanding at any one time.

It changes the maximum authority to $700 billion, in the aggregate, or such higher amount, in the aggregate, as has been obligated or expended under TARP as of the enactment of this Act.

The Act requires the Secretary to report to Congress every six months on transfer to the Treasury's General Fund for reduction of the public debt of revenues of, and proceeds from the sale of troubled assets purchased under TARP, or from the sale, exercise, or surrender of warrants or senior debt instruments acquired under TARP.

The Act makes changes to the Federal National Mortgage Association Charter Act, the Federal Home Loan Mortgage Corporation Act, and the Federal Home Loan Bank Act.

It requires that  the Secretary to deposit in the Treasury solely for debt reduction any amounts received by the Secretary for the sale of any obligation or security acquired from the Federal National Mortgage Association (Fannie Mae), the Federal Home Loan Mortgage Corporation (Freddie Mac), or a Federal Home Loan Bank for secondary market operations. It prohibits the use of any such amounts as an offset for other spending increases or revenue reductions.

It requires that it be deposited in the Treasury solely for debt reduction of any periodic commitment fee or any other fee or assessment paid to the Secretary by Fannie Mae or Freddie Mac as a result of any preferred stock purchase agreement, mortgage-backed security purchase program, or any other program or activity under the Housing and Economic Recovery Act of 2008. Requires the Director of the Federal Housing Finance Agency (FHFA) to report to Congress on FHFA plans to continue to support and maintain the nation's vital housing industry, while at the same time guaranteeing that the American taxpayer will not suffer unnecessary losses.

The Act amends the American Recovery and Reinvestment Act of 2009 (ARRA) to require:

• rescission of any ARRA (stimulus) funds offered to but not accepted by the governor or legislature of a state
• their deposit in the Treasury solely for debt reduction.

The Act requires the same treatment for any funds withdrawn or recaptured by an executive agency head which have not been obligated by a state to a local government or for a specific project.