than December 31, 2018, the Secretary of the Treasury or the Secretary's delegate (referred to in this section as the Secretary ) shall establish and implement a program (referred to in this section as the Refund to Rainy Day Savings Program ) to allow a participating taxpayer, pursuant to the requirements established under this section, to defer payment on 20 percent of the amount which would otherwise be refunded to such taxpayer as an overpayment (as described in section 6401 of the Internal Revenue Code of 1986). (b) Period of deferral Except as provided under subsection (c)(5), a participating taxpayer may elect to defer payment of the amount described in subsection (a) and have such amount deposited in the Rainy Day Fund (as described in subsection (c)). (c) Rainy Day Fund (1) In general The Secretary shall establish a fund, in such manner as the Secretary determines to be appropriate, to be known as the Rainy Day Fund , consisting of any amounts described in subsection (a) on which payment has been deferred by participating taxpayers. (2) Investment Any amounts deposited in the Rainy Day Fund shall be invested by the Secretary, in coordination with the Bureau of the Fiscal Service of the Department of the Treasury, in United States Treasury bills issued under chapter 31 of title 31, United States Code, with maturities suitable for the needs of the Fund and selected so as to provide the highest return on investment for participating taxpayers. (3) Disbursements from fund (A) In general On the date that is 180 days after receipt of the individual income tax return of a participating taxpayer, the amounts in the Rainy Day Fund shall be made available to the Secretary to distribute to such taxpayer in an amount equal to the amount deferred by such taxpayer under subsection (a) and any interest accrued on such amount (as determined under paragraph (4)). (B) Distributed to bank account The amounts described in subparagraph (A) shall be distributed to the bank account identified by the participating taxpayer