Calculating a gross or pretax rate of interest or dividend by adding a notional amount of tax to the net, or post-tax amount received. 
UK shareholders receive dividends with a tax credit of 10%. This means that a notional 10% tax... <a target=_blank href='http://www.finance-glossary.com/terms/grossing-up.htm?id=652&ginPtrCode=00000&PopupMode=false' title='Read full definition of grossing up'>more</a>
The term given to the process of adding back the tax deducted to the net income to calculate the gross income liable to tax.