Except as provided in pars. (b), (c) and (d), the amount of each installment required under sub. (12) is 25 percent of the lower of the following amounts: 1.
(1)#
Ninety percent of the tax shown on the return for the taxable year or, if no return is filed, 90 percent of the tax for the taxable year.
(2)#
The tax shown on the return for the preceding year. If a husband and wife who filed separate returns for the preceding taxable year file a joint return, the tax shown on the return for the preceding year is the sum of the taxes shown on the separate returns of the husband and wife. If a husband and wife who filed a joint return for the preceding taxable year file separate returns, the tax shown on the return for the preceding year is the husband’s or wife’s proportion of that tax based on what their respective tax liabilities for that year would have been had they filed separately.