insurance providers (a) Imposition of fee (1) In general Each covered entity engaged in the business of providing health insurance shall pay to the Secretary not later than the annual payment date of each calendar year beginning after 2018 a fee in an amount determined under subsection (b). (2) Annual payment date For purposes of this section, the term annual payment date means, with respect to any calendar year, a date determined by the Secretary, which in no event, may be later than September 30 of such calendar year. (b) Determination of fee amount With respect to each covered entity, the fee under this section for any calendar year shall be equal to the amount determined under section 17(a)(2), multiplied by the ratio of the covered entity’s net premiums written with respect to health insurance for any United States health risk taken into account under subsection (c) during the preceding calendar year, to— (1) the sum of net premiums for all covered entities