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 8.
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.
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.
