Media tycoon Berlusconi, 78, has been serving the order by helping out with Alzheimer's patients at the Cesano Boscone care home near Milan every Friday since last May.
The judge's decision to trim the sentence on good behaviour grounds means he will be freed from those duties on March 8th.
He will also then regain his freedom of movement, which was restricted under the order, enabling him to resume a higher-profile role in national politics despite still being banned from public office.
After a series of appeals, Berlusconi was finally convicted of tax fraud in August 2013. But for his advanced age, he would have been sent to prison.
He was allowed to retain the leadership of his Forza Italia party.
The centre right grouping retains considerable influence in parliament but has slipped badly in the opinion polls over the time Berlusconi has been making his visits to the care home.