Calculating federal income tax FIT can be confusing because it is not a flat tax but a progressive tax. There is software to help and the IRS provides table to help with the process. To use the table s we nee marital status, allowances, and pay periods. If the income it over a certain dollar amount we may not be able to use the tables but must use the percentage method. It is useful to calculate the federal income tax withholding FIT withholdings using the percentage method because it gives us a better idea of how the progressive tax system works, how different layers of wages are taxed at different rates. For more accounting Information see website http://accountinginstruction.info/cou…