The windfall tax will also help the Centre partly offset the impact of the excise duty cut. Central Board of Indirect Taxes and Customs chairman Vivek Chaturvedi said the windfall tax on exports will result in a gain of about Rs 1,500 crore in the first fortnight while the govt will have to forgo over Rs 7,000 crore in revenue because of the excise duty cut. He said the export tax will be reviewed fortnightly.