F-tax is a Swedish tax paid by self-employed person.
Entrepreneurs who carry on business activity as a one-man business usually have an F-tax card. This means that the entrepreneur himself has to pay his taxes and social security contributions (self-employed person's contributions) every month.
Irrespective of whether you pay A-tax, SA-tax or F-tax, the tax that you or your employer pay continuously throughout the year should as far as possible agree with your calculated final tax. You cannot decide yourself to pay in the tax in arrears.