Every insurer doing a life insurance business within this state, except fraternals as defined in s. 614.01, shall pay into the state treasury as an annual license fee for transacting such business the amounts following:

   (1)   Domestic insurers.

      (a)    If such insurer is organized under the laws of this state, it shall pay as an annual license fee 3.5 percent upon its gross income from all sources for the preceding calendar year except interest required to provide and maintain reserves according to the laws of this state, and except premiums collected on policies of insurance and contracts for annuities. No domestic insurer shall, however, in any year pay in the aggregate for license fee as prescribed in this paragraph an amount in excess of the annual license fee which would have been payable by it in such year under sub. (2) had it been operating as a foreign insurer subject to sub. (2). Any domestic insurer having in excess of $750,000,000 of insurance in force as of December 31 of the preceding calendar year, excluding therefrom any reinsurance assumed on which premium taxes are payable by the ceding insurer, shall not pay less in the aggregate for a license fee as prescribed in this paragraph than the amount of the annual license fee which would have been payable by it in such year under sub. (2) had it been operating as a foreign insurer subject to sub. (2). Payments under this paragraph shall be made annually on or before March 1.

      (b)    In computing the fee under par. (a), the amount of such gross income shall, after deducting the excepted portions thereof, be multiplied by a fraction the numerator of which is the net investment income applicable to life insurance and annuities and the denominator of which is the total net investment income, as set forth in the annual statement forms for such year as approved by the commissioner of insurance.

   (2)   Foreign insurers. If any such insurer is organized outside of this state, it shall pay into the state treasury, as such annual license fee, 2 percent upon the excess of the gross premiums received in money or otherwise during the preceding calendar year on all policies or contracts of insurance on the lives of residents of this state after deducting all sums apportioned to premium paying policies on the lives of residents of this state from annual distribution of profits, savings, earnings or surplus which before the expiration of the calendar year next succeeding such apportionment have been either paid in cash or applied in part payment of premiums.