Critical Access Hospital Flexibility Act of 2013 - Amends title XVIII (Medicare) of the Social Security Act (SSA) with respect to the Medicare rural hospital flexibility program and criteria for designation of critical access hospitals, specifically the requirement to provide not more than 25 acute care inpatient beds for inpatient care for up to 96 hours per patient as an annual average.

Permits a facility that was designated a critical access hospital before enactment of this Act, in the alternative, to satisfy such requirement by providing not more than 20 acute care inpatient beds.

Requires all beds to be occupied for the bed count to meet this critical access hospital criterion.