Anyone who realizes that their income this year is lower than what they declared for 2014, or that they have significant deductible or tax-deductible expenses, can request to pay less than the amount reported in the settlement statement (form 730-3), expressing their wish in writing to their employer or pension institution.
With the 730 form, advance payments for 2015 income, relating to personal income tax and/or the flat-rate tax, are calculated directly based on the income declared for the previous year and are, upon their due date, in this case in November, withheld by the withholding agent from the paycheck or pension installment.
In the liquidation statement, the amounts of the second or single advance payment of Irpef and the flat-rate tax are indicated, respectively, in lines 95 and 101 (115 and 121 for the declaring spouse).
However, if you want the withholding to be less severe (for example, because you've incurred many deductible expenses and believe your 2015 taxes should be reduced), or if you don't want it to be withheld at all, you can calculate the advance payment due yourself and communicate it in writing to your tax representative.
Taxpayers intending to take this route must, however, be careful to correctly calculate the amounts due. If, upon payment of the annual tax due for 2015 (with the corresponding tax return), the advance payments are found to be lower than the actual amount due, penalties for underpayment will be applied, equal to 30% of the difference between the amount paid and the amount due. In this case, before the Revenue Agency notifies the irregularity, it will be possible to remedy the situation by resorting to the "ravvedimento operoso" (voluntary disclosure), the rules for which were redesigned by the 2015 Stability Law (see "More Cooperation with Taxpayers. Unlimited Rectification").
Source: http://www.fiscooggi.it/attualita/article/riduzione-degli-acconti-730da-richiedere-entro-settembre
