a taxpayer who has classes 5-S income during a tax year will have to compute his tax liability twice a year. the first computation, interim computation, is to take income arising between january to june of a tax year and compute income tax using the methods explained above. he must file and pay taxes to the revenue department by the end of september. the interim tax paid can be used as a tax credit for the computation at the end of year. the form used is form 94 (por.ngor.dor. 94) the second computation is the end of year computation.the taxpayers bring into account all classes of income arising during the tax year. he will then compute his lax liability as explained above. he will have to file his tax returns and pay taxes, if any, to the revenue depertment by the end of march of the following year. the form used is form.90 (por.ngor.dor. 90).