42 CFR § 66.110 - Service, payback, and recovery requirements.
(a) Each individual who receives an Award for postdoctoral research or training shall engage in a month of research training, research, or teaching that is health-related (or any combination thereof) for each month of support received, up to a maximum of twelve months. Such period shall be served in accordance with the usual patterns of such employment or training.
(b) In any case in which an individual receives an Award for more than twelve months, the thirteenth month and each subsequent month of performing activities under the Award shall be considered to be activities toward satisfaction of the requirement established in paragraph (a) of this section.
(c) Except as provided in § 66.111, an individual subject to the requirements for service in paragraph (a) of this section must begin to undertake the service on a continuous basis within two years after the expiration or termination for his or her Award.
(d) If the individual fails to undertake or perform the service in accordance with the requirements of this section, the United States shall be entitled to recover from the individual an amount determined in accordance with the formula:
(e) Except as provided in § 66.111, the individual shall pay to the United States any amount which it is entitled to recover under paragraph (d) of this section within a three-year period beginning on the date the United States becomes entitled to recovery that amount. Interest shall accrue to the United States until any amount due it under paragraph (d) of the section is paid. The rate of interest will be fixed by the Secretary of the Treasury after taking into consideration private consumer rates of interest prevailing on the date the United States becomes entitled to recovery.